Bramble-bees and Others
by
J. Henri Fabre
Part 3 out of 5
which she strictly confines herself. The first has her leaves; the
second her wadding; the third her resin. None of these guilds has
ever changed trades with another; and none ever will. There you have
instinct, keeping the workers to their specialities. There are no
innovations in their workshops, no recipes resulting from experiment,
no ingenious devices, no progress from indifferent to good, from good
to excellent. To-day's method is the facsimile of yesterday's; and
to-morrow will know no other.
But, though the manufacturing-process is invariable, the raw material
is subject to change. The plant that supplies the cotton differs in
species according to the locality; the bush out of whose leaves the
pieces will be cut is not the same in the various fields of
operation; the tree that provides the resinous putty may be a pine, a
cypress, a juniper, a cedar or a spruce, all very different in
appearance. What will guide the insect in its gleaning? Discernment.
These, I think, are sufficient details of the fundamental distinction
to be drawn in the insect's mentality; the distinction, that is,
between instinct and discernment. If people confuse these two
provinces, as they nearly always do, any understanding becomes
impossible; the last glimmer of light disappears behind the clouds of
interminable discussions. From an industrial point of view, let us
look upon the insect as a worker thoroughly versed from birth in a
craft whose essential principles never vary; let us grant that
unconscious worker a gleam of intelligence which will permit it to
extricate itself from the inevitable conflict of attendant
circumstances; and I think that we shall have come as near to the
truth as the state of our knowledge will allow for the moment.
Having thus assigned a due share both to instinct and the aberrations
of instinct when the course of its different phases is disturbed, let
us see what discernment is able to do in the selection of a site for
the nest and materials for building it; and, leaving the Pelopaeus,
upon whom it is useless to dwell any longer, let us consider other
examples, picked from among those richest in variations.
The Mason-bee of the Sheds (Chalicodoma rufitarsis, PEREZ) well
deserves the name which I have felt justified in giving her from her
habits: she settles in numerous colonies in our sheds, on the lower
surface of the tiles, where she builds huge nests which endanger the
solidity of the roof. Nowhere does the insect display a greater zeal
for work than in one of these colossal cities, an estate which is
constantly increasing as it passes down from one generation to
another; nowhere does it find a better workshop for the exercise of
its industry. Here it has plenty of room: a quiet resting-place,
sheltered from damp and from excess of heat or cold.
But the spacious domain under the tiles is not within the reach of
all: sheds with free access and the proper sunny aspect are pretty
rare. These sites fall only to the favoured of fortune. Where will
the others take up their quarters? More or less everywhere. Without
leaving the house in which I live, I can enumerate stone, wood,
glass, metal, paint and mortar as forming the foundation of the
nests. The green-house with its furnace heat in the summer and its
bright light, equalling that outside, is fairly well-frequented. The
Mason-bee hardly ever fails to build there each year, in squads of a
few dozen apiece, now on the glass panes, now on the iron bars of the
framework. Other little swarms settle in the window embrasures, under
the projecting ledge of the front door or in the cranny between the
wall and an open shutter. Others again, being perhaps of a morose
disposition, flee society and prefer to work in solitude, one in the
inside of a lock or of a pipe intended to carry the rain-water from
the leads; another in the mouldings of the doors and windows or in
the crude ornamentation of the stone-work. In short, the house is
made use of all round, provided that the shelter be an out-of-door
one; for observe that the enterprising invader, unlike the Pelopaeus,
never penetrates inside our dwellings. The case of the conservatory
is an exception more apparent than real: the glass building, standing
wide open throughout the summer, is to the Mason-bee but a shed a
little lighter than the others. There is nothing here to arouse the
distrust with which anything indoors or shut up inspires her. To
build on the threshold of an outer door, or to usurp its lock, a
hiding-place to her fancy, is all that she allows herself; to go any
farther is an adventure repugnant to her taste.
Lastly, in the case of all these dwellings, the Mason-bee is man's
free tenant; her industry makes use of the products of our own
industry. Can she have no other establishments? She has, beyond a
doubt; she possesses some constructed on the ancient plan. On a stone
the size of a man's fist, protected by the shelter of a hedge,
sometimes even on a pebble in the open air, I see her building now
groups of cells as large as a walnut, now domes emulating in size,
shape and solidity those of her rival, the Mason-bee of the Walls.
The stone support is the most frequent, though not the only one. I
have found nests, but sparsely inhabited it is true, on the trunks of
trees, in the seams of the rough bark of oaks. Among those whose
support was a living plant, I will mention two that stand out above
all the others. The first was built in the lobe of a torch-thistle as
thick as my leg; the second rested on a stalk of the opuntia, the
Indian fig. Had the fierce armour of these two stout cactuses
attracted the attention of the insect, which looked upon their tufts
of spikes as furnishing a system of defence for its nest? Perhaps so.
In any case, the attempt was not imitated; I never saw another
installation of the kind. There is one definite conclusion to be
drawn from my two discoveries. Despite the oddity of their structure,
which is unparalleled among the local flora, the two American
importations did not compel the insect to go through an
apprenticeship of groping and hesitation. The one which found itself
in the presence of those novel growths, and which was perhaps the
first of its race to do so, took possession of their lobes and stalks
just as it would have done of a familiar site. From the start, the
fleshy plants from the New World suited it as well as the trunk of a
native tree.
The Mason-bee of the Pebbles (Chalicodoma parietina) has none of this
elasticity in the choice of a site. In her case, the smooth stone of
the parched uplands is the almost invariable foundation of her
structures. Elsewhere, under a less clement sky, she prefers the
support of a wall, which protects the nest against the prolonged
snows. Lastly, the Mason-bee of the Shrubs (Chalicodoma rufescens,
PEREZ) fixes her ball of clay to a twig of any ligneous plant, from
the thyme, the rock-rose and the heath to the oak, the elm and the
pine. The list of the sites that suit her would almost form a
complete catalogue of the ligneous flora.
The variety of places wherein the insect instals itself, so eloquent
of the part played by discernment in their selection, becomes still
more remarkable when it is accompanied by a corresponding variety in
the architecture of the cells. This is more particularly the case
with the Three-horned Osmia, who, as she uses clayey materials very
easily affected by the rain, requires, like the Pelopaeus, a dry
shelter for her cells, a shelter which she finds ready-made and uses
just as it is, after a few touches by way of sweeping and cleansing.
The homes which I see her adopt are especially the shells of Snails
that have died under the stone-heaps and in the low, unmortared walls
which support the cultivated earth of the hills in shelves or
terraces. The use of Snail-shells is accompanied by the no less
active use of the old cells of both the Mason-bee of the Sheds and of
certain Anthophorae (A. pilipes, A. parietina and A. personata).
We must not forget the reed, which is highly appreciated when--a rare
find--it appears under the requisite conditions. In its natural
state, the plant with the mighty hollow cylinders is of no possible
use to the Osmia, who knows nothing of the art of perforating a woody
wall. The gallery of an internode has to be wide open before the
insect can take possession of it. Also, the clean-cut stump must be
horizontal, otherwise the rain would soften the fragile edifice of
clay and soon lay it low; also, the stump must not be lying on the
ground and must be kept at some distance from the dampness of the
soil. We see therefore that, without the intervention of man,
involuntary in the vast majority of cases and deliberate only on the
experimenter's part, the Osmia would hardly ever find a reed-stump
suited to the installation of her family. It is to her a casual
acquisition, a home unknown to her race before men took it into their
heads to cut reeds and make them into hurdles for drying figs in the
sun.
How did the work of man's pruning-knife bring about the abandonment
of the natural lodging? How was the spiral staircase of the Snail-
shell replaced by the cylindrical gallery of the reed? Was the change
from one kind of house to another effected by gradual transitions, by
attempts made, abandoned, resumed, becoming more and more definite in
their results as generation succeeded generation? Or did the Osmia,
finding the cut reed that answered her requirements, instal herself
there straightway, scorning her ancient dwelling, the Snail-shell?
These questions called for a reply; and they have received one. Let
us describe how things happened.
Near Serignan are some great quarries of coarse limestone,
characteristic of the miocene formation of the Rhone valley. These
have been worked for many generations. The ancient public buildings
of Orange, notably the colossal frontage of the theatre whither all
the intellectual world once flocked to hear Sophocles' "Oedipus
Tyrannus," derive most of their material from these quarries. Other
evidence confirms what the similarity of the hewn stone tells us.
Among the rubbish that fills up the spaces between the tiers of
seats, they occasionally discover the Marseilles obol, a bit of
silver stamped with the four-spoked wheel, or a few bronze coins
bearing the effigy of Augustus or Tiberius. Scattered also here and
there among the monuments of antiquity are heaps of refuse,
accumulations of broken stones in which various Hymenoptera,
including the Three-horned Osmia in particular, take possession of
the dead Snail-shell.
The quarries form part of an extensive plateau which is so arid as to
be nearly deserted. In these conditions, the Osmia, at all times
faithful to her birth-place, has little or no need to emigrate from
her heap of stones and leave the shell for another dwelling which she
would have to go and seek at a distance. Since there are heaps of
stone there, she probably has no other dwelling than the Snail-shell.
Nothing tells us that the present-day generations are not descended
in the direct line from the generations contemporary with the
quarryman who lost his as or his obol at this spot. All the
circumstances seem to point to it: the Osmia of the quarries is an
inveterate user of Snail-shells; so far as heredity is concerned, she
knows nothing whatever of reeds. Well, we must place her in the
presence of these new lodgings.
I collect during the winter about two dozen well-stocked Snail-shells
and instal them in a quiet corner of my study, as I did at the time
of my enquiries into the distribution of the sexes. The little hive
with its front pierced with forty holes has bits of reed fitted to
it. At the foot of the five rows of cylinders I place the inhabited
shells and with these I mix a few small stones, the better to imitate
the natural conditions. I add an assortment of empty Snail-shells,
after carefully cleaning the interior so as to make the Osmia's stay
more pleasant. When the time comes for nest-building, the stay-at-
home insect will have, close beside the house of its birth, a choice
of two habitations: the cylinder, a novelty unknown to its race; and
the spiral staircase, the ancient ancestral home.
The nests were finished at the end of May and the Osmiae began to
answer my list of questions. Some, the great majority, settled
exclusively in the reeds; the others remained faithful to the Snail-
shell or else entrusted their eggs partly to the spirals and partly
to the cylinders. With the first, who were the pioneers of
cylindrical architecture, there was no hesitation that I could
perceive: after exploring the stump of reed for a time and
recognizing it as serviceable, the insect instals itself there and,
an expert from the first touch, without apprenticeship, without
groping, without any tendencies bequeathed by the long practice of
its predecessors, builds its straight row of cells on a very
different plan from that demanded by the spiral cavity of the shell
which increases in size as it goes on.
The slow school of the ages, the gradual acquisitions of the past,
the legacies of heredity count for nothing therefore in the Osmia's
education. Without any novitiate on its own part or that of its
forebears, the insect is versed straight away in the calling which it
has to pursue; it possesses, inseparable from its nature, the
qualities demanded by its craft: some which are invariable and belong
to the domain of instinct; others, flexible, belonging to the
province of discernment. To divide a free lodging into chambers by
means of mud partitions; to fill those chambers with a heap of
pollen-flour, with a few sups of honey in the central part where the
egg is to lie; in short, to prepare board and lodging for the
unknown, for a family which the mothers have never seen in the past
and will never see in the future: this, in its essential features, is
the function of the Osmia's instinct. Here, everything is
harmoniously, inflexibly, permanently preordained; the insect has but
to follow its blind impulse to attain the goal. But the free lodging
offered by chance varies exceedingly in hygienic conditions, in shape
and in capacity. Instinct, which does not choose, which does not
contrive, would, if it were alone, leave the insect's existence in
peril. To help her out of her predicament, in these complex
circumstances, the Osmia possesses her little stock of discernment,
which distinguishes between the dry and the wet, the solid and the
fragile, the sheltered and the exposed; which recognizes the worth or
the worthlessness of a site and knows how to sprinkle it with cells
according to the size and shape of the space at disposal. Here,
slight industrial variations are necessary and inevitable; and the
insect excels in them without any apprenticeship, as the experiment
with the native Osmia of the quarries has just proved.
Animal resources have a certain elasticity, within narrow limits.
What we learn from the animals' industry at a given moment is not
always the full measure of their skill. They possess latent powers
held in reserve for certain emergencies. Long generations can succeed
one another without employing them; but, should some circumstance
require it, suddenly those powers burst forth, free of any previous
attempts, even as the spark potentially contained in the flint
flashes forth independently of all preceding gleams. Could one who
knew nothing of the Sparrow but her nest under the eaves suspect the
ball-shaped nest at the top of a tree? Would one who knew nothing of
the Osmia save her home in the Snail-shell expect to see her accept
as her dwelling a stump of reed, a paper funnel, a glass tube? My
neighbour the Sparrow, impulsively taking it into her head to leave
the roof for the plane-tree, the Osmia of the quarries, rejecting her
natal cabin, the spiral of the shell, for my cylinder, alike show us
how sudden and spontaneous are the industrial variations of animals.
CHAPTER 7. ECONOMY OF ENERGY.
What stimulus does the insect obey when it employs the reserve powers
that slumber in its race? Of what use are its industrial variations?
The Osmia will yield us her secret with no great difficulty. Let us
examine her work in a cylindrical habitation. I have described in
full detail, in the foregoing pages, the structure of her nests when
the dwelling adopted is a reed-stump or any other cylinder; and I
will content myself here with recapitulating the essential features
of that nest-building.
We must first distinguish three classes of reeds according to their
diameter: the small, the medium-sized and the large. I call small
those whose narrow width just allows the Osmia to go about her
household duties without discomfort. She must be able to turn where
she stands in order to brush her abdomen and rub off its load of
pollen, after disgorging the honey in the centre of the heap of flour
already collected. If the width of the tube does not admit of this
operation, if the insect is obliged to go out and then come in again
backwards in order to place itself in a favourable posture for the
discharge of the pollen, then the reed is too narrow and the Osmia is
rather reluctant to accept it. The middle-sized reeds and a fortiori
the large ones leave the victualler entire liberty of action; but the
former do not exceed the width of a cell, a width agreeing with the
bulk of the future cocoon, whereas the latter, with their excessive
diameter, require more than one chamber on the same floor.
When free to choose, the Osmia settles by preference in the small
reeds. Here, the work of building is reduced to its simplest
expression and consists in dividing the tube by means of earthen
partitions into a straight row of cells. Against the partition
forming the back wall of the preceding cell the mother places first a
heap of honey and pollen; next, when the portion is seen to be
enough, she lays an egg in the centre of it. Then and then only she
resumes her plasterer's work and marks out the length of the new cell
with a mud partition. This partition in its turn serves as the rear-
wall of another chamber, which is first victualled and then closed;
and so on until the cylinder is sufficiently colonized and receives a
thick terminal stopper at its orifice. In a word, the chief
characteristic of this method of nest-building, the roughest of all,
is that the partition in front is not undertaken so long as the
victualling is still incomplete, or, in other words, that the
provisions and the egg are deposited before the Bee sets to work on
the partition.
At first sight, this latter detail hardly deserves attention: is it
not right to fill the pot before we put a lid on? The Osmia who owns
a medium-sized reed is not at all of this opinion; and other
plasterers share her views, as we shall see when we watch the
Odynerus building her nest. (A genus of Mason-wasps, the essays on
which have not yet been translated into English.--Translator's Note.)
Here we have an excellent illustration of one of those latent powers
held in reserve for exceptional occasions and suddenly brought into
play, although often very far removed from the insect's regular
methods. If the reed, without being of inordinate width from the
point of view of the cocoon, is nevertheless too spacious to afford
the Bee a suitable purchase against the wall at the moment when she
is disgorging honey and brushing off her load of pollen; the Osmia
altogether changes the order of her work; she sets up the partition
first and then does the victualling.
All round the inside of the tube she places a ring of mud, which, as
the result of her constant visits to the mortar, ends by becoming a
complete diaphragm minus an orifice at the side, a sort of round dog-
hole, just large enough for the insect to pass through. When the cell
is thus marked out and almost wholly closed, the Osmia attends to the
storing of her provisions and the laying of her eggs. Steadying
herself against the margin of the hole at one time with her fore-legs
and at another with her hind-legs, she is able to empty her crop and
to brush her abdomen; by pressing against it, she obtains a foothold
for her little efforts in these various operations. When the tube was
narrow, the outer wall supplied this foothold and the earthen
partition was postponed until the heap of provisions was completed
and surmounted by the egg; but in the present case the passage is too
wide and would leave the insect floundering helplessly in space, so
the partition with its serving-hatch takes precedence of the
victuals. This method is a little more expensive than the other,
first in materials, because of the diameter of the reed, and secondly
in time, if only because of the dog-hole, a delicate piece of mortar-
work which is too soft at first and cannot be used until it has dried
and become harder. Therefore the Osmia, who is sparing of her time
and strength, accepts medium-sized reeds only when there are no small
ones available.
The large tubes she will use only in grave emergencies and I am
unable to state exactly what these exceptional circumstances are.
Perhaps she decides to make use of those roomy dwellings when the
eggs have to be laid at once and there is no other shelter in the
neighbourhood. While my cylinder-hives gave me plenty of well-filled
reeds of the first and second class, they provided me with but half-
a-dozen at most of the third, notwithstanding my precaution to
furnish the apparatus with a varied assortment.
The Osmia's repugnance to big cylinders is quite justified. The work
in fact is longer and more costly when the tubes are wide. An
inspection of a nest constructed under these conditions is enough to
convince us. It now consists not of a string of chambers obtained by
simple transverse partitions, but of a confused heap of clumsy, many-
sided compartments, standing back to back, with a tendency to group
themselves in storeys without succeeding in doing so, because any
regular arrangement would mean that the ceilings possessed a span
which it is not in the builder's power to achieve. The edifice is not
a geometrical masterpiece and it is even less satisfactory from the
point of view of economy. In the previous constructions, the sides of
the reed supplied the greater part of the walls and the work was
limited to one partition for each cell. Here, except at the actual
periphery, where the tube itself supplies a foundation, everything
has to be obtained by sheer building: the floor, the ceiling, the
walls of the many-sided compartment are one and all made of mortar.
The structure is almost as costly in materials as that of the
Chalicodoma or the Pelopaeus.
It must be pretty difficult, too, when one thinks of its
irregularity. Fitting as best she can the projecting angles of the
new cell into the recessed corners of the cell already built, the
Osmia runs up walls more or less curved, upright or slanting, which
intersect one another at various points, so that each compartment
requires a new and complicated plan of construction, which is very
different from the circular-partition style of architecture, with its
row of parallel dividing-disks. Moreover, in this composite
arrangement, the size of the recesses left available by the earlier
work to some extent decides the assessment of the sexes, for,
according to the dimensions of those recesses, the walls erected take
in now a larger space, the home of a female, and now a smaller space,
the home of a male. Roomy quarters therefore have a double drawback
for the Osmia: they greatly increase the outlay in materials; and
also they establish in the lower layers, among the females, males
who, because of their earlier hatching, would be much better placed
near the mouth of the nest. I am convinced of it: if the Osmia
refuses big reeds and accepts them only in the last resort, when
there are no others, it is because she objects to additional labour
and to the mixture of the sexes.
The Snail-shell, then, is but an indifferent home for her, which she
is quite ready to abandon should a better offer. Its expanding cavity
represents an average between the favourite small cylinder and the
unpopular large cylinder, which is accepted only when there is no
other obtainable. The first whorls of the spiral are too narrow to be
of use to the Osmia, but the middle ones have the right diameter for
cocoons arranged in single file. Here things happen as in a first-
class reed, for the helical curve in no way affects the method of
structure employed for a rectilinear series of cells. Circular
partitions are erected at the required distances, with or without a
serving-hatch, according to the diameter. These mark out the first
cells, one after the other, which are reserved solely for the
females. Then comes the last whorl, which is much too wide for a
single row of cells; and here we once more find, exactly as in a wide
reed, a costly profusion of masonry, an irregular arrangement of the
cells and a mixture of the sexes.
Having said so much, let us go back to the Osmia of the quarries.
Why, when I offer them simultaneously Snail-shells and reeds of a
suitable size, do the old frequenters of the shells prefer the reeds,
which in all probability have never before been utilized by their
race? Most of them scorn the ancestral dwelling and enthusiastically
accept my reeds. Some, it is true, take up their quarters in the
Snail-shell; but even among these a goodly number refuse my new
shells and return to their birth-place, the old Snail-shell, in order
to utilize the family property, without much labour, at the cost of a
few repairs. Whence, I ask, comes this general preference for the
cylinder, never used hitherto? The answer can be only this: of two
lodgings at her disposal the Osmia selects the one that provides a
comfortable home at a minimum outlay. She economizes her strength
when restoring an old nest; she economizes it when replacing the
Snail-shell by the reed.
Can animal industry, like our own, obey the law of economy, the
sovran law that governs our industrial machine even as it governs, at
least to all appearances, the sublime machine of the universe? Let us
go deeper into the question and bring other workers into evidence,
those especially who, better equipped perhaps and at any rate better
fitted for hard work, attack the difficulties of their trade boldly
and look down upon alien establishments with scorn. Of this number
are the Chalicodomae, the Mason-bees proper.
The Mason-bee of the Pebbles does not make up her mind to build a
brand-new dome unless there be a dearth of old and not quite
dilapidated nests. The mothers, sisters apparently and heirs-at-law
to the domain, dispute fiercely for the ancestral abode. The first
who, by sheer brute force, takes possession of the dome, perches upon
it and, for long hours, watches events while polishing her wings. If
some claimant puts in an appearance, forthwith the other turns her
out with a volley of blows. In this way the old nests are employed so
long as they have not become uninhabitable hovels.
Without being equally jealous of the maternal inheritance, the Mason-
bee of the Sheds eagerly uses the cells whence her generation issued.
The work in the huge city under the eaves begins thus: the old cells,
of which, by the way, the good-natured owner yields a portion to
Latreille's Osmia and to the Three-horned Osmia alike, are first made
clean and wholesome and cleared of broken plaster and then
provisioned and shut. When all the accessible chambers are occupied,
the actual building begins with a new stratum of cells upon the
former edifice, which becomes more and more massive from year to
year.
The Mason-bee of the Shrubs, with her spherical nests hardly larger
than walnuts, puzzled me at first. Does she use the old buildings or
does she abandon them for good? To-day perplexity makes way for
certainty: she uses them very readily. I have several times surprised
her lodging her family in the empty rooms of a nest where she was
doubtless born herself. Like her kinswoman of the Pebbles, she
returns to the native dwelling and fights for its possession. Also,
like the dome-builder, she is an anchorite and prefers to cultivate
the lean inheritance alone. Sometimes, however, the nest is of
exceptional size and harbours a crowd of occupants, who live in
peace, each attending to her business, as in the colossal hives in
the sheds. Should the colony be at all numerous and the estate
descend to two or three generations in succession, with a fresh layer
of masonry each year, the normal walnut-sized nest becomes a ball as
large as a man's two fists. I have gathered on a pine-tree a nest of
the Mason-bee of the Shrubs that weighed a kilogram (2.205 pounds
avoirdupois.--Translator's Note.) and was the size of a child's head.
A twig hardly thicker than a straw served as its support. The casual
sight of that lump swinging over the spot on which I had sat down
made me think of the mishap that befell Garo. (The hero of La
Fontaine's fable, "Le Gland et la Citrouille," who wondered why
acorns grew on such tall trees and pumpkins on such low vines, until
he fell asleep under one of the latter and a pumpkin dropped upon his
nose.--Translator's Note.) If such nests were plentiful in the trees,
any one seeking the shade would run a serious risk of having his head
smashed.
After the Masons, the Carpenters. Among the guild of wood-workers,
the most powerful is the Carpenter-bee (Xylocopa violacea (Cf. "The
Life of the Spider": chapter 1.--Translator's Note.)), a very large
Bee of formidable appearance, clad in black velvet with violet-
coloured wings. The mother gives her larvae as a dwelling a
cylindrical gallery which she digs in rotten wood. Useless timber
lying exposed to the air, vine-poles, large logs of fire-wood
seasoning out of doors, heaped up in front of the farmhouse porch,
stumps of trees, vine-stocks and big branches of all kinds are her
favourite building-yards. A solitary and industrious worker, she
bores, bit by bit, circular passages the width of one's thumb, as
clear-cut as though they were made with an auger. A heap of saw-dust
accumulates on the ground and bears witness to the severity of the
task. Usually, the same aperture is the entrance to two or three
parallel corridors. With several galleries there is accommodation for
the entire laying, though each gallery is quite short; and the Bee
thus avoids those long series which always create difficulties when
the moment of hatching arrives. The laggards and the insects eager to
emerge are less likely to get in each other's way.
After obtaining the dwelling, the Carpenter-bee behaves like the
Osmia who is in possession of a reed. Provisions are collected, the
egg is laid and the chamber is walled in front with a saw-dust
partition. The work is pursued in this way until the two or three
passages composing the house are completely stocked. Heaping up
provisions and erecting partitions are an invariable feature of the
Xylocopa's programme; no circumstance can release the mother from the
duty of providing for the future of her family, in the matter both of
ready-prepared food and of separate compartments for the rearing of
each larva. It is only in the boring of the galleries, the most
laborious part of the work, that economy can occasionally be
exercised by a piece of luck. Well, is the powerful Carpenter, all
unheeding of fatigue, able to take advantage of such fortunate
occasions? Does she know how to make use of houses which she has not
tunnelled herself? Why, yes: a free lodging suits her just as much as
it does the various Mason-bees. She knows as well as they the
economic advantages of an old nest that is still in good condition:
she settles down, as far as possible, in her predecessors' galleries,
after freshening up the sides with a superficial scraping. And she
does better still. She readily accepts lodgings which have never
known a drill, no matter whose. The stout reeds used in the trellis-
work that supports the vines are valuable discoveries, providing as
they do sumptuous galleries free of cost. No preliminary work or next
to none is required with these. Indeed, the insect does not even
trouble to make a side-opening, which would enable it to occupy the
cavity contained within two nodes; it prefers the opening at the end
cut by man's pruning-knife. If the next partition be too near to give
a chamber of sufficient length, the Xylocopa destroys it, which is
easy work, not to be compared with the labour of cutting an entrance
through the side. In this way, a spacious gallery, following on the
short vestibule made by the pruning-knife, is obtained with the least
possible expenditure of energy.
Guided by what was happening on the trellises, I offered the black
Bee the hospitality of my reed-hives. From the very beginning, the
insect gladly welcomed my advances; each spring, I see it inspect my
rows of cylinders, pick out the best ones and instal itself there.
Its work, reduced to a minimum by my intervention, is limited to the
partitions, the materials for which are obtained by scraping the
inner sides of the reed.
As first-rate joiners, next to the Carpenter-bees come the Lithurgi,
of whom my district possesses two species: L. cornutus, FAB., and L.
chrysurus, BOY. By what aberration of nomenclature was the name of
Lithurgus, a worker in stone, given to insects which work solely in
wood? I have caught the first, the stronger of the two, digging
galleries in a large block of oak that served as an arch for a
stable-door; I have always found the second, who is more widely
distributed, settling in dead wood--mulberry, cherry, almond, poplar-
-that was still standing. Her work is exactly the same as the
Xylocopa's, on a smaller scale. A single entrance-hole gives access
to three or four parallel galleries, assembled in a serried group;
and these galleries are subdivided into cells by means of saw-dust
partitions. Following the example of the big Carpenter-bee, Lithurgus
chrysurus knows how to avoid the laborious work of boring, when
occasion offers: I find her cocoons lodged almost as often in old
dormitories as in new ones. She too has the tendency to economize her
strength by turning the work of her predecessors to account. I do not
despair of seeing her adopt the reed if, one day, when I possess a
large enough colony, I decide to try this experiment on her. I will
say nothing about L. cornutus, whom I only once surprised at her
carpentering.
The Anthophorae, those children of the precipitous earthy banks, show
the same thrifty spirit as the other members of the mining
corporation. Three species, A. parietina, A. personata and A.
pilipes, dig long corridors leading to the cells, which are scattered
here and there and one by one. These passages remain open at all
seasons of the year. When spring comes, the new colony uses them just
as they are, provided that they are well preserved in the clayey mass
baked by the sun; it increases their length if necessary, runs out a
few more branches, but does not decide to start boring in new ground
until the old city, which, with its many labyrinths, resembles some
monstrous sponge, is too much undermined for safety. The oval niches,
the cells that open on those corridors, are also profitably employed.
The Anthophora restores their entrance, which has been destroyed by
the insect's recent emergence; she smooths their walls with a fresh
coat of whitewash, after which the lodging is fit to receive the heap
of honey and the egg. When the old cells, insufficient in number and
moreover partly inhabited by diverse intruders, are all occupied, the
boring of new cells begins, in the extended sections of the
galleries, and the rest of the eggs are housed. In this way, the
swarm is settled at a minimum of expense.
To conclude this brief account, let us change the zoological setting
and, as we have already spoken of the Sparrow, see what he can do as
a builder. The simplest form of his nest is the great round ball of
straw, dead leaves and feathers, in the fork of a few branches. It is
costly in material, but can be set up anywhere, when the hole in the
wall or the shelter of a tile are lacking. What reasons induced him
to give up the spherical edifice? To all seeming, the same reasons
that led the Osmia to abandon the Snail-shell's spiral, which
requires a fatiguing expenditure of clay, in favour of the economical
cylinder of the reed. By making his home in a hole in the wall, the
Sparrow escapes the greater part of his work. Here, the dome that
serves as a protection from the rain and the thick walls that offer
resistance to the wind both become superfluous. A mere mattress is
sufficient; the cavity in the wall provides the rest. The saving is
great; and the Sparrow appreciates it quite as much as the Osmia.
This does not mean that the primitive art has disappeared, lost
through neglect; it remains an ineffaceable characteristic of the
species, ever ready to declare itself should circumstances demand it.
The generations of to-day are as much endowed with it as the
generations of yore; without apprenticeship, without the example of
others, they have within themselves, in the potential state, the
industrial aptitude of their ancestors. If aroused by the stimulus of
necessity, this aptitude will pass suddenly from inaction to action.
When, therefore, the Sparrow still from time to time indulges in
spherical building, this is not progress on his part, as is sometimes
contended; it is, on the contrary, a retrogression, a return to the
ancient customs, so prodigal of labour. He is behaving like the Osmia
who, in default of a reed, makes shift with a Snail-shell, which is
more difficult to utilize but easier to find. The cylinder and the
hole in the wall stand for progress; the spiral of the Snail-shell
and the ball-shaped nest represent the starting-point.
I have, I think, sufficiently illustrated the inference which is
borne out by the whole mass of analogous facts. Animal industry
manifests a tendency to achieve the essential with a minimum of
expenditure; after its own fashion, the insect bears witness to the
economy of energy. On the one hand, instinct imposes upon it a craft
that is unchangeable in its fundamental features; on the other hand,
it is left a certain latitude in the details, so as to take advantage
of favourable circumstances and attain the object aimed at with the
least possible expenditure of time, materials and work, the three
elements of mechanical labour. The problem in higher geometry solved
by the Hive-bee is only a particular case--true, a magnificent case,-
-of this general law of economy which seems to govern the whole
animal world. The wax cells, with their maximum capacity as against a
minimum wall-space, are the equivalent, with the superaddition of a
marvellous scientific skill, of the Osmia's compartments in which the
stonework is reduced to a minimum through the selection of a reed.
The artificer in mud and the artificer in wax obey the same tendency:
they economize. Do they know what they are doing? Who would venture
to suggest it in the case of the Bee grappling with her
transcendental problem? The others, pursuing their rustic art, are no
wiser. With all of them, there is no calculation, no premeditation,
but simply blind obedience to the law of general harmony.
CHAPTER 8. THE LEAF-CUTTERS.
It is not enough that animal industry should be able, to a certain
extent, to adapt itself to casual exigencies when choosing the site
of a nest; if the race is to thrive, something else is required,
something which hide-bound instinct is unable to provide. The
Chaffinch, for instance, introduces a great quantity of lichen into
the outer layer of his nest. This is his method of strengthening the
edifice and making a stout framework in which to place first the
bottom mattress of moss, fine straw and rootlets and then the soft
bed of feathers, wool and down. But, should the time-honoured lichen
be lacking, will the bird refrain from building its nest? Will it
forgo the delight of hatching its brood because it has not the
wherewithal to settle its family in the orthodox fashion?
No, the chaffinch is not perplexed by so small a matter; he is an
expert in materials, he understands botanical equivalents. In the
absence of the branches of the evernias, he picks the long beards of
the usneas, the wartlike rosettes of the parmelias, the membranes of
the stictises torn away in shreds; if he can find nothing better, he
makes shift with the bushy tufts of the cladonias. As a practical
lichenologist, when one species is rare or lacking in the
neighbourhood, he is able to fall back on others, varying greatly in
shape, colour and texture. And, if the impossible happened and lichen
failed entirely, I credit the Chaffinch with sufficient talent to be
able to dispense with it and to build the foundations of his nest
with some coarse moss or other.
What the worker in lichens tells us the other weavers of textile
materials confirm. Each has his favourite flora, which hardly ever
varies when the plant is easily accessible and which can be
supplemented by plenty of others when it is not. The bird's botany
would be worth examining; it would be interesting to draw up the
industrial herbal of each species. In this connection, I will quote
just one instance, so as not to stray too far from the subject in
hand.
The Red-backed Shrike (Lanius collurio), the commonest variety in my
district, is noteworthy because of his savage mania for forked
gibbets, the thorns in the hedgerows whereon he impales the
voluminous contents of his game-bag--little half-fledged birds, small
Lizards, Grasshoppers, caterpillars, Beetles--and leaves them to get
high. To this passion for the gallows, which has passed unnoticed by
the country-folk, at least in my part, he adds another, an innocent
botanical passion, which is so much in evidence that everybody, down
to the youngest bird's-nester, knows all about it. His nest, a
massive structure, is made of hardly any other materials than a
greyish and very fluffy plant, which is found everywhere among the
corn. This is the Filago spathulata of the botanists; and the bird
also makes use, though less frequently, of the Filago germanica, or
common cotton-rose. Both are known in Provencal by the name herbo dou
tarnagas, or Shrike-herb. This popular designation tells us plainly
how faithful the bird is to its plant. To have struck the
agricultural labourer, a very indifferent observer, the Shrike's
choice of materials must be remarkably persistent.
Have we here a taste that is exclusive? Not in the least. Though
cotton-roses of all species are plentiful on level ground, they
become scarce and impossible to find on the parched hills. The bird,
on its side, is not given to journeys of exploration and takes what
it finds to suit it in the neighbourhood of its tree or hedge. But on
arid ground, the Micropus erectus, or upright micropus, abounds and
is a satisfactory substitute for the Filago so far as its tiny,
cottony leaves and its little fluffy balls of flowers are concerned.
True, it is short and does not lend itself well to weaver's work. A
few long sprigs of another cottony plant, the Helichrysum staechas,
or wild everlasting, inserted here and there, will give body to the
structure. Thus does the Shrike manage when hard up for his favourite
materials: keeping to the same botanical family, he is able to find
and employ substitutes among the fine cotton-clad stalks.
He is even able to leave the family of the Compositae and to go
gleaning more or less everywhere. Here is the result of my
botanizings at the expense of his nests. We must distinguish between
two genera in the Shrike's rough classification: the cottony plants
and the smooth plants. Among the first, my notes mention the
following: Convolvulus cantabrica, or flax-leaved bindweed; Lotus
symmetricus, or bird's-foot trefoil; Teucrium polium, or poly; and
the flowery heads of the Phragmites communis, or common reed. Among
the second are these: Medicago lupulina, or nonesuch; Trifolium
repens, or white clover; Lathyrus pratensis, or meadow lathyrus;
Capsella bursa pastoris, or shepherd's purse; Vicia peregrina, or
broad-podded vetch; Convolvulus arvensis, or small bindweed;
Pterotheca nemausensis, a sort of hawkweed; and Poa pratensis, or
smooth-stalked meadow-grass. When it is downy, the plant forms almost
the whole nest, as is the case with the flax-leaved bindweed; when
smooth, it forms only the framework, destined to support a crumbling
mass of micropus, as is the case with the small bindweed. When making
this collection, which I am far from giving as the birds' complete
herbarium, I was struck by a wholly unexpected detail: of the various
plants, I found only the heads still in bud; moreover, all the
sprigs, though dry, possessed the green colouring of the growing
plant, a sign of swift desiccation in the sun. Save in a few cases,
therefore, the Shrike does not collect the dead and withered remains:
it is from the growing plants that he reaps his harvest, mowing them
down with his beak and leaving the sheaves to dry in the sun before
using them. I caught him one day hopping about and pecking at the
twigs of a Biscayan bindweed. He was getting in his hay, strewing the
ground with it.
The evidence of the Shrike, confirmed by that of all the other
workers--weavers, basket-makers or woodcutters--whom we may care to
call as witnesses, shows us what a large part must be assigned to
discernment in the bird's choice of materials for its nest. Is the
insect as highly gifted? When it works with vegetable matter, is it
exclusive in its tastes? Does it know only one definite plant, its
special province? Or has it, for employment in its manufactures, a
varied flora, in which its discernment exercises a free choice? For
answers to these questions we may look, above all, to the Leaf-
cutting Bees, the Megachiles. Reaumur has told the story of their
industry in detail; and I refer the reader who wishes for further
particulars to the master's Memoirs.
The man who knows how to use his eyes in his garden will observe,
some day or other, a number of curious holes in the leaves of his
lilac- and rose-trees, some of them round, some oval, as if idle but
skilful hands had been at work with the pinking-iron. In some places,
there is scarcely anything but the veins of the leaves left. The
author of the mischief is a grey-clad Bee, a Megachile. For scissors,
she has her mandibles; for compasses, producing now an oval and anon
a circle, she has her eye and the pivot of her body. The pieces cut
out are made into thimble-shaped wallets, destined to contain the
honey and the egg: the larger, oval pieces supply the floor and
sides; the smaller, round pieces are reserved for the lid. A row of
these thimbles, placed one on top of the other, up to a dozen or
more, though often there are less: that is, roughly, the structure of
the Leaf-cutter's nest.
When taken out of the recess in which the mother has manufactured it,
the cylinder of cells seems to be an indivisible whole, a sort of
tunnel obtained by lining with leaves some gallery dug underground.
The real thing does not correspond with its appearance: under the
least pressure of the fingers, the cylinder breaks up into equal
sections, which are so many compartments independent of their
neighbours as regards both floor and lid. This spontaneous break up
shows us how the work is done. The method agrees with those adopted
by the other Bees. Instead of a general scabbard of leaves,
afterwards subdivided into compartments by transverse partitions, the
Megachile constructs a string of separate wallets, each of which is
finished before the next is begun.
A structure of this sort needs a sheath to keep the pieces in place
while giving them the proper shape. The bag of leaves, in fact, as
turned out by the worker, lacks stability; its numerous pieces, not
glued together, but simply placed one after the other, come apart and
give way as soon as they lose the support of the tunnel that keeps
them united. Later, when it spins its cocoon, the larva infuses a
little of its fluid silk into the gaps and solders the pieces to one
another, especially the inner ones, so much so that the insecure bag
in due course becomes a solid casket whose component parts it is no
longer possible to separate entirely.
The protective sheath, which is also a framework, is not the work of
the mother. Like the great majority of the Osmiae, the Megachiles do
not understand the art of making themselves a home straight away:
they want a borrowed lodging, which may vary considerably in
character. The deserted galleries of the Anthophorae, the burrows of
the fat Earth-worms, the tunnels bored in the trunks of trees by the
larva of the Cerambyx-beetle (The Capricorn, the essay on which has
not yet been published in English.--Translator's Note.), the ruined
dwellings of the Mason-bee of the Pebbles, the Snail-shell nests of
the Three-horned Osmia, reed-stumps, when these are handy, and
crevices in the walls are all so many homes for the Leaf-cutters, who
choose this or that establishment according to the tastes of their
particular genus.
For the sake of clearness, let us cease generalizing and direct our
attention to a definite species. I first selected the White-girdled
Leaf-cutter (Megachile albocincta, PEREZ), not on account of any
exceptional peculiarities, but solely because this is the Bee most
often mentioned in my notes. Her customary dwelling is the tunnel of
an Earth-worm opening on some clay bank. Whether perpendicular or
slanting, this tunnel runs down to an indefinite depth, where the
climate would be too damp for the Bee. Besides, when the time comes
for the hatching of the adult insect, its emergence would be fraught
with peril if it had to climb up from a deep pit through crumbling
rubbish. The Leaf-cutter, therefore, uses only the front portion of
the Worm's gallery, two decimetres at most. (7.8 inches.--
Translator's Note.) What is to be done with the rest of the tunnel?
It is an ascending shaft, tempting to an enemy; and some underground
ravager might come this way and destroy the nest by attacking the row
of cells at the back.
The danger is foreseen. Before fashioning her first honey-bag, the
Bee blocks the passage with a strong barricade composed of the only
materials used in the Leaf-cutter's guild. Fragments of leaves are
piled up in no particular order, but in sufficient quantities to make
a serious obstacle. It is not unusual to find in the leafy rampart
some dozens of pieces rolled into screws and fitting into one another
like a stack of cylindrical wafers. For this work of fortification,
artistic refinement seems superfluous; at any rate, the pieces of
leaves are for the most part irregular. You can see that the insect
has cut them out hurriedly, unmethodically and on a different pattern
from that of the pieces intended for the cells.
I am struck with another detail in the barricade. Its constituents
are taken from stout, thick, strong-veined leaves. I recognize young
vine-leaves, pale-coloured and velvety; the leaves of the whitish
rock-rose (Cistus albidus), lined with a hairy felt; those of the
holm-oak, selected among the young and bristly ones; those of the
hawthorn, smooth but tough; those of the cultivated reed, the only
one of the Monocotyledones exploited, as far as I know, by the
Megachiles. In the construction of cells, on the other hand, I see
smooth leaves predominating, notably those of the wild briar and of
the common acacia, the robinia. It would appear, therefore, that the
insect distinguishes between two kinds of materials, without being an
absolute purist and sternly excluding any sort of blending. The very
much indented leaves, whose projections can be completely removed
with a dexterous snip of the scissors, generally furnish the various
layers of the barricade; the little robinia-leaves, with their fine
texture and their unbroken edges, are better suited to the more
delicate work of the cells.
A rampart at the back of the Earth-worm's shaft is a wise precaution
and the Leaf-cutter deserves all credit for it; only it is a pity for
the Megachiles' reputation that this protective barrier often
protects nothing at all. Here we see, under a new guise, that
aberration of instinct of which I gave some examples in an earlier
chapter. My notes contain memoranda of various galleries crammed with
pieces of leaves right up to the orifice, which is on a level with
the ground, and entirely devoid of cells, even of an unfinished one.
These were ridiculous fortifications, of no use whatever; and yet the
Bee treated the matter with the utmost seriousness and took infinite
pains over her futile task. One of these uselessly barricaded
galleries furnished me with some hundred pieces of leaves arranged
like a stack of wafers; another gave me as many as a hundred and
fifty. For the defence of a tenanted nest, two dozen and even fewer
are ample. Then what was the object of the Leaf-cutter's ridiculous
pile?
I wish I could believe that, seeing that the place was dangerous, she
made her heap bigger so that the rampart might be in proportion to
the danger. Then, perhaps, at the moment of starting on the cells,
she disappeared, the victim of an accident, blown out of her course
by a gust of wind. But this line of defence is not admissible in the
Megachile's case. The proof is palpable: the galleries aforesaid are
barricaded up to the level of the ground; there is no room,
absolutely none, to lodge even a single egg. What was her object, I
ask again, when she persisted in obstinately piling up her wafers?
Has she really an object?
I do not hesitate to say no. And my answer is based upon what the
Osmiae taught me. I have described above how the Three-horned Osmia,
towards the end of her life, when her ovaries are depleted, expends
on useless operations such energy as remains to her. Born a worker,
she is bored by the inactivity of retirement; her leisure requires an
occupation. Having nothing better to do, she sets up partitions; she
divides a tunnel into cells that will remain empty; she closes with a
thick plug reeds containing nothing. Thus is the modicum of strength
of her decline exhausted in vain labours. The other Builder-bees
behave likewise. I see Anthidia laboriously provide numerous bales of
cotton to stop galleries wherein never an egg was laid; I see
Mason-bees build and then religiously close cells that will remain
unvictualled and uncolonized.
The long and useless barricades then belong to the last hours of the
Megachile's life, when the eggs are all laid; the mother, whose
ovaries are exhausted, persists in building. Her instinct is to cut
out and heap up pieces of leaves; obeying this impulse, she cuts out
and heaps up even when the supreme reason for this labour ceases. The
eggs are no longer there, but some strength remains; and that
strength is expended as the safety of the species demanded in the
beginning. The wheels of action go on turning in the absence of the
motives for action; they continue their movement as though by a sort
of acquired velocity. What clearer proof can we hope to find of the
unconsciousness of the animal stimulated by instinct?
Let us return to the Leaf-cutter's work under normal conditions.
Immediately after a protective barrier comes the row of cells, which
vary considerably in number, like those of the Osmia in her reed.
Strings of about a dozen are rare; the most frequent consist of five
or six. No less subject to variation is the number of pieces joined
to make a cell: pieces of two kinds, some, the oval ones, forming the
honey-pot; others, the round ones, serving as a lid. I count, on an
average, eight to ten pieces of the first kind. Though all cut on the
pattern of an ellipse, they are not equal in dimensions and come
under two categories. The larger, outside ones are each of them
almost a third of the circumference and overlap one another slightly.
Their lower end bends into a concave curve to form the bottom of the
bag. Those inside, which are considerably smaller, increase the
thickness of the sides and fill up the gaps left by the first.
The Leaf-cutter therefore is able to use her scissors according to
the task before her: first, the large pieces, which help the work
forward, but leave empty spaces; next, the small pieces, which fit
into the defective portions. The bottom of the cell particularly
comes in for after-touches. As the natural curve of the larger pieces
is not enough to provide a cup without cracks in it, the Bee does not
fail to improve the work with two or three small oval pieces applied
to the imperfect joins.
Another advantage results from the snippets of unequal size. The
three or four outer pieces, which are the first placed in position,
being the longest of all, project beyond the mouth, whereas the next,
being shorter, do not come quite up to it. A brim is thus obtained, a
ledge on which the round disks of the lid rest and are prevented from
touching the honey when the Bee presses them into a concave cover. In
other words, at the mouth the circumference comprises only one row of
leaves; lower down it takes two or three, thus restricting the
diameter and securing an hermetic closing.
The cover of the pot consists solely of round pieces, very nearly
alike and more or less numerous. Sometimes I find only two, sometimes
I count as many as ten, closely stacked. At times, the diameter of
these pieces is of an almost mathematical precision, so much so that
the edges of the disk rest upon the ledge. No better result would be
obtained had they been cut out with the aid of compasses. At times,
again, the piece projects slightly beyond the mouth, so that, to
enter, it has to be pressed down and curved cupwise. There is no
variation in the diameter of the first pieces placed in position,
those nearest to the honey. They are all of the same size and thus
form a flat cover which does not encroach on the cell and will not
afterwards interfere with the larva, as a convex ceiling would. The
subsequent disks, when the pile is numerous, are a little larger;
they only fit the mouth by yielding to pressure and becoming concave.
The Bee seems to make a point of this concavity, for it serves as a
mould to receive the curved bottom of the next cell.
When the row of cells is finished, the task still remains of blocking
up the entrance to the gallery with a safety-stopper similar to the
earthen plug with which the Osmia closes her reeds. The Bee then
returns to the free and easy use of the scissors which we noticed at
the beginning when she was fencing off the back part of the Earth-
worm's too deep burrow; she cuts out of the foliage irregular pieces
of different shapes and sizes and often retaining their original
deeply-indented margins; and with all these pieces, very few of which
fit at all closely the orifice to be blocked, she succeeds in making
an inviolable door, thanks to the huge number of layers.
Let us leave the Leaf-cutter to finish depositing her eggs in other
galleries, which will be colonized in the same manner, and consider
for a moment her skill as a cutter. Her edifices consist of a
multitude of fragments belonging to three categories: oval pieces for
the sides of the cells; round pieces for the lids; and irregular
pieces for the barricades at the front and back. The last present no
difficulty: the Bee obtains them by removing from the leaf some
projecting portion, as it stands, a serrate lobe which, owing to its
notches, shortens the insect's task and lends itself better to
scissor-work. So far, there is nothing to deserve attention: it is
unskilled labour, in which an inexperienced apprentice might excel.
With the oval pieces, it becomes another matter. What model has the
Megachile when cutting her neat ellipses out of the delicate material
for her wallets, the robinia-leaves? What mental pattern guides her
scissors? What system of measurement tells her the dimensions? One
would like to picture the insect as a living pair of compasses,
capable of tracing an elliptic curve by a certain natural inflexion
of its body, even as our arm traces a circle by swinging from the
shoulder. A blind mechanism, the mere outcome of its organization,
would alone be responsible for its geometry. This explanation would
tempt me if the large oval pieces were not accompanied by much
smaller ones, also oval, which are used to fill the empty spaces. A
pair of compasses which changes its radius of its own accord and
alters the curve according to the plan before it appears to me an
instrument somewhat difficult to believe in. There must be something
better than that. The circular pieces of the lid suggest it to us.
If, by the mere flexion inherent in her structure, the Leaf-cutter
succeeds in cutting out ovals, how does she succeed in cutting out
rounds? Can we admit the presence of other wheels in the machinery
for the new pattern, so different in shape and size? Besides, the
real point of the difficulty does not lie there. These rounds, for
the most part, fit the mouth of the jar with almost exact precision.
When the cell is finished, the Bee flies hundreds of yards away to
make the lid. She arrives at the leaf from which the disk is to be
cut. What picture, what recollection has she of the pot to be
covered? Why, none at all: she has never seen it; she does her work
underground, in utter darkness! At the utmost, she can have the
indications of touch: not actual indications, of course, for the pot
is not there, but past indications, useless in a work of precision.
And yet the disk to be cut out must have a fixed diameter: if it were
too large, it would not go in; if too small, it would close badly, it
would slip down on the honey and suffocate the egg. How shall it be
given its correct dimensions without a pattern? The Bee does not
hesitate for a moment. She cuts out her disk with the same celerity
which she would display in detaching any shapeless lobe that might do
for a stopper; and that disk, without further measurement, is of the
right size to fit the pot. Let whoso will explain this geometry,
which in my opinion is inexplicable, even when we allow for memory
begotten of touch and sight.
One winter evening, as we were sitting round the fire, whose cheerful
blaze unloosed our tongues, I put the problem of the Leaf-cutter to
my family:
'Among your kitchen-utensils,' I said, 'you have a pot in daily use;
but it has lost its lid, which was knocked over and broken by the
Tomcat playing among the shelves. To-morrow is market-day and one of
you will be going to Orange to buy the week's provisions. Would she
undertake, without a measure of any kind, with the sole aid of
memory, which we would allow her to refresh before starting by a
careful examination of the object, to bring back exactly what the pot
wants, a lid neither too large nor too small, in short the same size
as the top?'
It was admitted with one accord that nobody would accept such a
commission without taking a measure with her, or at least a bit of
string giving the width. Our memory for sizes is not accurate enough.
She would come back from the town with something that 'might do'; and
it would be the merest chance if this turned out to be the right
size.
Well, the Leaf-cutter is even less well-off than ourselves. She has
no mental picture of her pot, because she has never seen it; she is
not able to pick and choose in the crockery-dealer's heap, which acts
as something of a guide to our memory by comparison; she must,
without hesitation, far away from her home, cut out a disk that fits
the top of her jar. What is impossible to us is child's-play to her.
Where we could not do without a measure of some kind, a bit of
string, a pattern or a scrap of paper with figures upon it, the
little Bee needs nothing at all. In housekeeping matters she is
cleverer than we are.
One objection was raised. Was it not possible that the Bee, when at
work on the shrub, should first cut a round piece of an approximate
diameter, larger than that of the neck of the jar, and that
afterwards, on returning home, she should gnaw away the superfluous
part until the lid exactly fitted the pot? These alterations made
with the model in front of her would explain everything.
That is perfectly true; but are there any alterations? To begin with,
it seems to me hardly possible that the insect can go back to the
cutting once the piece is detached from the leaf: it lacks the
necessary support to gnaw the flimsy disk with any precision. A
tailor would spoil his cloth if he had not the support of a table
when cutting out the pieces for a coat. The Megachile's scissors, so
difficult to wield on anything not firmly held, would do equally bad
work.
Besides, I have better evidence than this for my refusal to believe
in the existence of alterations when the Bee has the cell in front of
her. The lid is composed of a pile of disks whose number sometimes
reaches half a score. Now the bottom part of all these disks is the
under surface of the leaf, which is paler and more strongly veined;
the top part is the upper surface, which is smooth and greener. In
other words, the insect places them in the position which they occupy
when gathered. Let me explain. In order to cut out a piece, the Bee
stands on the upper surface of the leaf. The piece detached is held
in the feet and is therefore laid with its top surface against the
insect's chest at the moment of departure. There is no possibility of
its being turned over on the journey. Consequently, the piece is laid
as the Bee has just picked it, with the lower surface towards the
inside of the cell and the upper surface towards the outside. If
alterations were necessary to reduce the lid to the diameter of the
pot, the disk would be bound to get turned over: the piece,
manipulated, set upright, turned round, tried this way and that,
would, when finally laid in position, have its top or bottom surface
inside just as it happened to come. But this is exactly what does not
take place. Therefore, as the order of stacking never changes, the
disks are cut, from the first clip of the scissors, with their proper
dimensions. The insect excels us in practical geometry. I look upon
the Leaf-cutter's pot and lid as an addition to the many other
marvels of instinct that cannot be explained by mechanics; I submit
it to the consideration of science; and I pass on.
The Silky Leaf-cutter (Megachile sericans, FONSCOL.; M. Dufourii,
LEP.) makes her nests in the disused galleries of the Anthophorae. I
know her to occupy another dwelling which is more elegant and affords
a more roomy installation: I mean the old dwelling of the fat
Capricorn, the denizen of the oaks. The metamorphosis is effected in
a spacious chamber lined with soft felt. When the long-horned Beetle
reaches the adult stage, he releases himself and emerges from the
tree by following a vestibule which the larva's powerful tools have
prepared beforehand. When the deserted cabin, owing to its position,
remains wholesome and there is no sign of any running from its walls,
no brown stuff smelling of the tan-yard, it is soon visited by the
Silky Megachile, who finds in it the most sumptuous of the apartments
inhabited by the Leaf-cutters. It combines every condition of
comfort: perfect safety, an even temperature, freedom from damp,
ample room; and so the mother who is fortunate enough to become the
possessor of such a lodging uses it entirely, vestibule and drawing-
room alike. Accommodation is found for all her family of eggs; at
least, I have nowhere seen nests as populous as here.
One of them provides me with seventeen cells, the highest number
appearing in my census of the Megachile clan. Most of them are lodged
in the nymphal chamber of the Capricorn; and, as the spacious recess
is too wide for a single row, the cells are arranged in three
parallel series. The remainder, in a single string, occupy the
vestibule, which is completed and filled up by the terminal
barricade. In the materials employed, hawthorn-and paliurus-leaves
predominate. The pieces, both in the cells and in the barrier, vary
in size. It is true that the hawthorn-leaves, with their deep
indentations, do not lend themselves to the cutting of neat oval
pieces. The insect seems to have detached each morsel without
troubling overmuch about the shape of the piece, so long as it was
big enough. Nor has it been very particular about arranging the
pieces according to the nature of the leaf: after a few bits of
paliurus come bits of vine and hawthorn; and these again are followed
by bits of bramble and paliurus. The Bee has collected her pieces
anyhow, taking a bit here and there, just as her fancy dictated.
Nevertheless, paliurus is the commonest, perhaps for economical
reasons.
I notice, in fact, that the leaves of this shrub, instead of being
used piecemeal, are employed whole, when they do not exceed the
proper dimensions. Their oval form and their moderate size suit the
insect's requirements; and there is therefore no necessity to cut
them into pieces. The leaf-stalk is clipped with the scissors and,
without more ado, the Megachile retires the richer by a first-rate
bit of material.
Split up into their component parts, two cells give me altogether
eighty-three pieces of leaves, whereof eighteen are smaller than the
others and of a round shape. The last-named come from the lids. If
they average forty-two each, the seventeen cells of the nest
represent seven hundred and fourteen pieces. These are not all: the
nest ends, in the Capricorn's vestibule, with a stout barricade in
which I count three hundred and fifty pieces. The total therefore
amounts to one thousand and sixty-four. All those journeys and all
that work with the scissors to furnish the deserted chamber of the
Cerambyx! If I did not know the Leaf-cutter's solitary and jealous
disposition, I should attribute the huge structure to the
collaboration of several mothers; but there is no question of
communism in this case. One dauntless creature and one alone, one
solitary, inveterate worker, has produced the whole of the prodigious
mass. If work is the best way to enjoy life, this one certainly has
not been bored during the few weeks of her existence.
I gladly award her the most honourable of eulogies, that due to the
industrious; and I also compliment her on her talent for closing the
honey-pots. The pieces stacked into lids are round and have nothing
to suggest those of which the cells and the final barricade are made.
Excepting the first, those nearest the honey, they are perhaps cut a
little less neatly than the disks of the White-girdled Leaf-cutter;
no matter: they stop the jar perfectly, especially when there are
some ten of them one above the other. When cutting them, the Bee was
as sure of her scissors as a dressmaker guided by a pattern laid on
the stuff; and yet she was cutting without a model, without having in
front of her the mouth to be closed. To enlarge on this interesting
subject would mean to repeat oneself. All the Leaf-cutters have the
same talent for making the lids of their pots.
A less mysterious question than this geometrical problem is that of
the materials. Does each species of Megachile keep to a single plant,
or has it a definite botanical domain wherein to exercise its liberty
of choice? The little that I have already said is enough to make us
suspect that the insect is not restricted to one plant; and this is
confirmed by an examination of the separate cells, piece by piece,
when we find a variety which we were far from imagining at first.
Here is the flora of the Megachiles in my neighbourhood, a very
incomplete flora and doubtless capable of considerable amplification
by future researches.
The Silky Leaf-cutter gathers the materials for her pots, her lids
and her barricades from the following plants: paliurus, hawthorn,
vine, wild briar, bramble, holm-oak, amelanchier, terebinthus, sage-
leaved rock-rose. The first three supply the greater part of the
leaf-work; the last three are represented only by rare fragments.
The Hare-footed Leaf-cutter (Megachile lagopoda, LIN.) which I see
very busy in my enclosure, though she only collects her materials
there, exploits the lilac and the rose-tree by preference. From time
to time, I see her also cutting bits out of the robinia, the quince-
tree and the cherry-tree. In the open country, I have found her
building with the leaves of the vine alone.
The Silvery Leaf-cutter (Megachile argentata, FAB.), another of my
guests, shares the taste of the aforesaid for the lilac and the rose,
but her domain includes in addition the pomegranate-tree, the
bramble, the vine, the common dogwood and the cornelian cherry.
The White-girdled Leaf-cutter likes the robinia, to which she adds,
in lavish proportions, the vine, the rose and the hawthorn and
sometimes, in moderation, the reed and the whitish-leaved rock-rose.
The Black-tipped Leaf-cutter (Megachile apicalis, SPIN.) has for her
abode the cells of the Mason-bee of the Pebbles and the ruined nests
of the Osmiae and Anthidia in the Snail-shells. I have not known her
to use any other materials than the wild briar and the hawthorn.
Incomplete though it be, this list tells us that the Megachiles do
not have exclusive botanical tastes. Each species manages extremely
well with several plants differing greatly in appearance. The first
condition to be fulfilled by the shrub exploited is that it be near
the nest. Frugal of her time, the Leaf-cutter declines to go on
distant expeditions. Whenever I come upon a recent Megachile-nest, I
am not long in finding in the neighbourhood, without much searching,
the tree or shrub from which the Bee has cut her pieces.
Another main condition is a fine and supple texture, especially for
the first disks used in the lid and for the pieces which form the
lining of the wallet. The rest, less carefully executed, allows of
coarser stuff; but even then the piece must be flexible and lend
itself to the cylindrical configuration of the tunnel. The leaves of
the rock-roses, thick and roughly fluted, fulfil this condition
unsatisfactorily, for which reason I see them occurring only at very
rare intervals. The insect has gathered pieces of them by mistake
and, not finding them good to use, has ceased to visit the
unprofitable shrub. Stiffer still, the leaf of the holm-oak in its
full maturity is never employed: the Silky Leaf-cutter uses it only
in the young state and then in moderation; she can get her velvety
pieces better from the vine. In the lilac-bushes so zealously
exploited before my eyes by the Hare-footed Leaf-cutter occur a
medley of different shrubs which, from their size and the lustre of
their leaves, should apparently suit that sturdy pinker. They are the
shrubby hare's-ear, the honeysuckle, the prickly butcher's-broom, the
box. What magnificent disks ought to come from the hare's-ear and the
honeysuckle! One could get an excellent piece, without further
labour, by merely cutting the leaf-stalk of the box, as Megachile
sericans does with her paliurus. The lilac-lover disdains them
absolutely. For what reason? I fancy that she finds them too stiff.
Would she think differently if the lilac-bush were not there? Perhaps
so.
In short, apart from the questions of texture and proximity to the
nest, the Megachile's choice, it seems to me, must depend upon
whether a particular shrub is plentiful or not. This would explain
the lavish use of the vine, an object of widespread cultivation, and
of the hawthorn and the wild briar, which form part of all our
hedges. As these are to be found everywhere, the fact that the
different Leaf-cutters make use of them is no reflection upon a host
of equivalents varying according to the locality.
If we had to believe what people tell us about the effects of
heredity, which is said to hand down from generation to generation,
ever more firmly established, the individual habits of those who come
before, the Megachiles of these parts, experienced in the local flora
by the long training of the centuries, but complete novices in the
presence of plants which their race encounters for the first time,
ought to refuse as unusual and suspicious any exotic leaves,
especially when they have at hand plenty of the leaves made familiar
by hereditary custom. The question was deserving of separate study.
Two subjects of my observations, the Hare-footed and the Silvery
Leaf-cutter, both of them inmates of my open-air laboratory, gave me
a definite answer. Knowing the points frequented by the two
Megachiles, I planted in their work-yard, overgrown with briar and
lilac, two outlandish plants which seemed to me to fulfil the
required conditions of suppleness of texture, namely, the ailantus, a
native of Japan, and the Virginian physostegia. Events justified the
selection: both Bees exploited the foreign flora with the same
assiduity as the local flora, passing from the lilac to the ailantus,
from the briar to the physostegia, leaving the one, going back to the
other, without drawing distinctions between the known and the
unknown. Inveterate habit could not have given greater certainty,
greater ease to their scissors, though this was their first
experience of such a material.
The Silvery Leaf-cutter lent herself to an even more conclusive test.
As she readily makes her nest in the reeds of my apparatus, I was
able, up to a certain point, to create a landscape for her and select
its vegetation myself. I therefore moved the reed-hive to a part of
the enclosure stocked chiefly with rosemary, whose scanty foliage is
not adapted for the Bee's work, and near the apparatus I arranged an
exotic shrubbery in pots, including notably the smooth lopezia, from
Mexico, and the long-fruited capsicum, an Indian annual. Finding
close at hand the wherewithal to build her nest, the Leaf-cutter went
no further afield. The lopezia suited her especially, so much so that
almost the whole nest was composed of it. The rest had been gathered
from the capsicum.
Another recruit, whose co-operation I had in no way engineered, came
spontaneously to offer me her evidence. This was the Feeble Leaf-
cutter (Megachile imbecilla, GERST.). Nearly a quarter of a century
ago, I saw her, all through the month of July, cutting out her rounds
and ellipses at the expense of the petals of the Pelargonium zonale,
the common geranium. Her perseverance devastated--there is no other
word for it--my modest array of pots. Hardly was a blossom out, when
the ardent Megachiles came and scalloped it into crescents. The
colour was indifferent to her: red, white or pink, all the petals
underwent the disastrous operation. A few captures, ancient relics of
my collecting-boxes by this time, indemnified me for the pillage. I
have not seen this unpleasant Bee since. With what does she build
when there are no geranium-flowers handy? I do not know; but the fact
remains that the fragile tailoress used to attack the foreign flower,
a fairly recent acquisition from the Cape, as though all her race had
never done anything else.
These details leave us with one obvious conclusion, which is contrary
to our original ideas, based on the unvarying character of insect
industry. In constructing their jars, the Leaf-cutters, each
following the taste peculiar to her species, do not make use of this
or that plant to the exclusion of the others; they have no definite
flora, no domain faithfully transmitted by heredity. Their pieces of
leaves vary according to the surrounding vegetation; they vary in
different layers of the same cell. Everything suits them, exotic or
native, rare or common, provided that the bit cut out be easy to
employ. It is not the general aspect of the shrub, with its fragile
or bushy branches, its large or small, green or grey, dull or glossy
leaves, that guides the insect: such advanced botanical knowledge
does not enter into the question at all. In the thicket chosen as a
pinking-establishment, the Megachile sees but one thing: leaves
useful for her work. The Shrike, with his passion for plants with
long, woolly sprigs, knows where to find nicely-wadded substitutes
when his favourite growth, the cotton-rose, is lacking; the Megachile
has much wider resources: indifferent to the plant itself, she looks
only into the foliage. If she finds leaves of the proper size, of a
dry texture capable of defying the damp and of a suppleness
favourable to cylindrical curving, that is all she asks; and the rest
does not matter. She has therefore an almost unlimited field for her
labour.
These sudden and wholly unprovoked changes give cause for reflection.
When my geranium-flowers were devastated, how had the obtrusive Bee,
untroubled by the profound dissimilarity between the petals, snow-
white here, bright scarlet there, how had she learnt her trade?
Nothing tells us that she herself was not for the first time
exploiting the plant from the Cape; and, if she really did have
predecessors, the habit had not had time to become inveterate,
considering the modern importation of the geranium. Where again did
the Silvery Megachile, for whom I created an exotic shrubbery, make
the acquaintance of the lopezia, which comes from Mexico? She
certainly is making a first start. Never did her village or mine
possess a stalk of that chilly denizen of our hot-houses. She is
making a first start; and behold her straightway a graduate, versed
in the art of carving unfamiliar foliage.
People often talk of the long apprenticeships served by instinct, of
its gradual acquirements, of its talents, the laborious work of the
ages. The Megachiles affirm the exact opposite. They tell me that the
animal, though invariable in the essence of its art, is capable of
innovation in the details; but at the same time they assure me that
any such innovation is sudden and not gradual. Nothing prepares the
innovations, nothing improves them or hands them down; otherwise a
selection would long ago have been made amid the diversity of
foliage; and the shrub recognized as the most serviceable, especially
when it is also plentiful, would alone supply all the building-
materials needed. If heredity transmitted industrial discoveries, a
Megachile who thought of cutting her disks out of pomegranate-leaves
and found them satisfactory ought to have instilled a liking for
similar materials into her descendants; and we should this day find
Leaf-cutters faithful to the pomegranate-leaves, workers who remained
exclusive in their choice of the raw material. The facts refute these
theories.
People also say:
'Grant us a variation, however small, in the insect's industry; and
that variation, accentuated more and more, will produce a new race
and finally a fixed species.'
This trifling variation is the fulcrum for which Archimedes clamoured
in order to lift the world with his system of levers. The Megachiles
offer us one and a very great one: the indefinite variation of their
materials. What will the theorists' levers lift with this fulcrum?
Why, nothing at all! Whether they cut the delicate petals of the
geranium or the tough leaves of the lilac-bushes, the Leaf-cutters
are and will be what they were. This is what we learn from the
persistence of each species in its structural details, despite the
great variety of the foliage employed.
CHAPTER 9. THE COTTON-BEES.
The evidence of the Leaf-cutters proves that a certain latitude is
left to the insect in its choice of materials for the nest; and this
is confirmed by the testimony of the Anthidia, the cotton-
manufacturers. My district possesses five: A. Florentinum, LATR., A.
diadema, LATR., A. manicatum, LATR., A. cingulatum, LATR., A.
scapulare, LATR. None of them creates the refuge in which the cotton
goods are manufactured. Like the Osmiae and the Leaf-cutters, they
are homeless vagrants, adopting, each to her own taste, such shelter
as the work of others affords. The Scapular Anthidium is loyal to the
dry bramble, deprived of its pith and turned into a hollow tube by
the industry of various mining Bees, among which figure, in the front
rank, the Ceratinae, dwarf rivals of the Xylocopa, or Carpenter-bee,
that mighty driller of rotten wood. The spacious galleries of the
Masked Anthophora suit the Florentine Anthidium, the foremost member
of the genus so far as size is concerned. The Diadem Anthidium
considers that she has done very well if she inherits the vestibule
of the Hairy-footed Anthophora, or even the ordinary burrow of the
Earth-worm. Failing anything better, she may establish herself in the
dilapidated dome of the Mason-bee of the Pebbles. The Manicate
Anthidium shares her tastes. I have surprised the Girdled Anthidium
cohabiting with a Bembex-wasp. The two occupants of the cave dug in
the sand, the owner and the stranger, were living in peace, both
intent upon their business. Her usual habitation is some hole or
other in the crevices of a ruined wall. To these refuges, the work of
others, we can add the stumps of reeds, which are as popular with the
various cotton-gatherers as with the Osmiae; and, after we have
mentioned a few most unexpected retreats, such as the sheath provided
by a hollow brick or the labyrinth furnished by the lock of a gate,
we shall have almost exhausted the list of domiciles.
Like the Osmiae and the Leaf-cutters, the Anthidium shows an urgent
need of a ready-made home. She never houses herself at her own
expense. Can we discover the reason? Let us first consult a few hard
workers who are artificers of their own dwellings. The Anthophora
digs corridors and cells in the road-side banks hardened by the sun;
she does not erect, she excavates; she does not build, she clears.
Toiling away with her mandibles, atom by atom, she manages to
contrive the passages and chambers necessary for her eggs; and a huge
business it is. She has, in addition, to polish and glaze the rough
sides of her tunnels. What would happen if, after obtaining a home by
dint of long-continued toil, she had next to line it with wadding, to
gather the fibrous down from cottony plants and to felt it into bags
suitable for the honey-paste? The hard-working Bee would not be equal
to producing all these refinements. Her mining calls for too great an
expenditure of time and strength to leave her the leisure for
luxurious furnishing. Chambers and corridors, therefore, will remain
bare.
The Carpenter-bee gives us the same answer. When with her joiner's
wimble she has patiently bored the beam to a depth of nine inches,
would she be able to cut out and place in position the thousand and
one pieces which the Silky Leaf-cutter employs for her nest? Time
would fail her, even as it would fail a Megachile who, lacking the
Capricorn's chamber, had herself to dig a home in the trunk of the
oak. Therefore the Carpenter-bee, after the tedious work of boring,
gets the installation done in the most summary fashion, simply
running up a sawdust partition.
The two things, the laborious business of obtaining a lodging and the
artistic work of furnishing, seem unable to go together. With the
insect as with man, he who builds the house does not furnish it, he
who furnishes it does not build it. To each his share, because of
lack of time. Division of labour, the mother of the arts, makes the
workman excel in his department; one man for the whole work would
mean stagnation, the worker never getting beyond his first crude
attempts. Animal industry is a little like our own: it does not
attain its perfection save with the aid of obscure toilers, who,
without knowing it, prepare the final masterpiece. I see no other
reason for this need of a gratuitous lodging for the Megachile's
leafy basket or the Anthidia's cotton purses. In the case of other
artists who handle delicate things that require protection, I do not
hesitate to assume the existence of a ready-made home. Thus Reaumur
tells us of the Upholsterer-bee, Anthocopa papaveris, who fashions
her cells with poppy-petals. I do not know the flower-cutter, I have
never seen her; but her art tells me plainly enough that she must
establish herself in some gallery wrought by others, as, for
instance, in an Earth-worm's burrow.
We have but to see the nest of a Cotton-bee to convince ourselves
that its builder cannot at the same time be an indefatigable navvy.
When and newly-felted and not yet made sticky with honey, the wadded
purse is by far the most elegant known specimen of entomological
nest-building, especially where the cotton is of a brilliant white,
as is frequently the case in the manufacturers of the Girdled
Anthidium. No bird's-nest, however deserving of our admiration, can
vie in fineness of flock, in gracefulness of form, in delicacy of
felting with this wonderful bag, which our fingers, even with the aid
of tools, could hardly imitate, for all their dexterity. I abandon
the attempt to understand how, with its little bales of cotton
brought up one by one, the insect, no otherwise gifted than the
kneaders of mud and the makers of leafy baskets, manages to felt what
it has collected into a homogeneous whole and then to work the
product into a thimble-shaped wallet. Its tools as a master-fuller
are its legs and its mandibles, which are just like those possessed
by the mortar-kneaders and Leaf-cutters; and yet, despite this
similarity of outfit, what a vast difference in the results obtained!
To see the Cotton-bees' talents in action seems an undertaking
fraught with innumerable difficulties: things happen at a depth
inaccessible to the eye; and to persuade the insect to work in the
open does not lie in our power. One resource remained and I did not
fail to turn to it, though hitherto I have been wholly unsuccessful.
Three species, Anthidium diadema, A. manicatum and A. florentinum--
the first-named in particular--show themselves quite ready to take up
their abode in my reed-apparatus. All that I had to do was to replace
the reeds by glass tubes, which would allow me to watch the work
without disturbing the insect. This stratagem had answered perfectly
with the Three-horned Osmia and Latreille's Osmia, whose little
housekeeping-secrets I had learnt thanks to the transparent dwelling-
house. Why should it not answer for its Cotton-bees and, in the same
way, with the Leaf-cutters? I almost counted on success. Events
betrayed my confidence. For four years I supplied my hives with glass
tubes and not once did the Cotton-weavers or the Leaf-cutters
condescend to take up their quarters in the crystal palaces. They
always preferred the hovel provided by the reed. Shall I persuade
them one day? I do not abandon all hope.
Meanwhile, let me describe the little that I saw. More or less
stocked with cells, the reed is at last closed, right at the orifice,
with a thick plug of cotton, usually coarser than the wadding of the
honey-satchels. It is the equivalent of the Three-horned Osmia's
barricade of mud, of the leaf-putty of Latreille's Osmia, of the
Megachiles' barrier of leaves cut into disks. All these free tenants
are careful to shut tight the door of the dwelling, of which they
have often utilized only a portion. To watch the building of this
barricade, which is almost external work, demands but a little
patience in waiting for the favourable moment.
The Anthidium arrives at last, carrying the bale of cotton for the
plugging. With her fore-legs she tears it apart and spreads it out;
with her mandibles, which go in closed and come out open, she loosens
the hard lumps of flock; with her forehead she presses each new layer
upon the one below. And that is all. The insect flies off, returns
the richer by another bale and repeats the performance until the
cotton barrier reaches the level of the opening. We have here,
remember, a rough task, in no way to be compared with the delicate
manufacturer of the bags; nevertheless, it may perhaps tell us
something of the general procedure of the finer work. The legs do the
carding, the mandibles the dividing, the forehead the pressing; and
the play of these implements produces the wonderful cushioned wallet.
That is the mechanism in the lump; but what of the artistry?
Let us leave the unknown for facts within the scope of observation. I
will question the Diadem Anthidium in particular, a frequent inmate
of my reeds. I open a reed-stump about two decimetres long by twelve
millimetres in diameter. (About seven and three-quarter inches by
half an inch.--Translator's Note.) The end is occupied by a column of
cotton-wool comprising ten cells, without any demarcation between
them on the outside, so that their whole forms a continuous cylinder.
Moreover, thanks to a close felting, the different compartments are
soldered together, so much so that, when pulled by the end, the
cotton edifice does not break into sections, but comes out all in one
piece. One would take it for a single cylinder, whereas in reality
the work is composed of a series of chambers, each of which has been
constructed separately, independently of the one before, except
perhaps at the base.
For this reason, short of ripping up the soft dwelling, still full of
honey, it is impossible to ascertain the number of storeys; we must
wait until the cocoons are woven. Then our fingers can tell the cells
by counting the knots that resist pressure under the cover of
wadding. This general structure is easily explained. A cotton bag is
made, with the sheath of the reed as a mould. If this guiding sheath
were lacking, the thimble shape would be obtained all the same, with
no less elegance, as is proved by the Girdled Anthidium, who makes
her nest in some hiding-place or other in the walls or the ground.
When the purse is finished, the provisions come and the egg, followed
by the closing of the cell. We do not here find the geometrical lid
of the Leaf-cutters, the pile of disks tight-set in the mouth of the
jar. The bag is closed with a cotton sheet whose edges are soldered
by a felting-process to the edges of the opening. The soldering is so
well done that the honey-pouch and its cover form an indivisible
whole. Immediately above it, the second cell is constructed, having
its own base. At the beginning of this work, the insect takes care to
join the two storeys by felting the ceiling of the first to the floor
of the second. Thus continued to the end, the work, with its inner
solderings, becomes an unbroken cylinder, in which the beauties of
the separate wallets disappear from view. In very much the same
fashion, but with less adhesion among the different cells, do the
Leaf-cutters act when stacking their jars in a column without any
external division into storeys.
Let us return to the reed-stump which gives us these details. Beyond
the cotton-wool cylinder wherein ten cocoons are lodged in a row
comes an empty space of half a decimetre or more. (About two inches.-
-Translator's Note.) The Osmiae and the Leaf-cutters are also
accustomed to leave these long, deserted vestibules. The nest ends,
at the orifice of the reed, with a strong plug of flock coarser and
less white than that of the cells. This use of closing-materials
which are less delicate in texture but of greater resisting-power,
while not an invariable characteristic, occurs frequently enough to
make us suspect that the insect knows how to distinguish what is best
suited now to the snug sleeping-berth of the larvae, anon to the
defensive barricade of the home. Sometimes the choice is an
exceedingly judicious one, as is shown by the nest of the Diadem
Anthidium. Time after time, whereas the cells were composed of the
finest grade of white cotton, gathered from Centaurea solsticialis,
or St. Barnaby's thistle, the barrier at the entrance, differing from
the rest of the work in its yellow colouring, was a heap of close-set
bristles supplied by the scallop-leaved mullein. The two functions of
the wadding are here plainly marked. The delicate skin of the larvae
needs a well-padded cradle; and the mother collects the softest
materials that the cottony plants provide. Rivalling the bird, which
furnishes the inside of the nest with wool and strengthens the
outside with sticks, she reserves for the grubs' mattress the finest
down, so hard to find and collected with such patience. But, when it
becomes a matter of shutting the door against the foe, then the
entrance bristles with forbidding caltrops, with stiff, prickly
hairs.
This ingenious system of defence is not the only one known to the
Anthidia. More distrustful still, the Manicate Anthidium leaves no
space in the front part of the reed. Immediately after the column of
cells, she heaps up, in the uninhabited vestibule, a conglomeration
of rubbish, whatever chance may offer in the neighbourhood of the
nest: little pieces of gravel, bits of earth, grains of sawdust,
particles of mortar, cypress-catkins, broken leaves, dry Snail-
droppings and any other material that comes her way. The pile, a real
barricade this time, blocks the reed completely to the end, except
about two centimetres (About three-quarters of an inch.--Translator's
Note.) left for the final cotton plug. Certainly no foe will break in
through the double rampart; but he will make an insidious attack from
the rear. The Leucopsis will come and, with her long probe, thanks to
some imperceptible fissure in the tube, will insert her dread eggs
and destroy every single inhabitant of the fortress. Thus are the
Manicate Anthidium's anxious precautions outwitted.
If we had not already seen the same thing with the Leaf-cutters, this
would be the place to enlarge upon the useless tasks undertaken by
the insect when, with its ovaries apparently depleted, it goes on
spending its strength with no maternal object in view and for the
sole pleasure of work. I have come across several reeds stopped up
with flock though containing nothing at all, or else furnished with
one, two or three cells devoid of provisions or eggs. The ever-
imperious instinct for gathering cotton and felting it into purses
and heaping it into barricades persists, fruitlessly, until life
fails. The Lizard's tail wriggles, curls and uncurls after it is
detached from the animal's body. In these reflex movements, I seem to
see not an explanation, certainly, but a rough image of the
industrious persistency of the insect, still toiling away at its
business, even when there is nothing useful left to do. This worker
knows no rest but death.
I have said enough about the dwelling of the Diadem Anthidium; let us
look at the inhabitant and her provisions. The honey is pale-yellow,
homogeneous and of a semifluid consistency, which prevents it from
trickling through the porous cotton bag. The egg floats on the
surface of the heap, with the end containing the head dipped into the
paste. To follow the larva through its progressive stages is not
without interest, especially on account of the cocoon, which is one
of the most singular that I know. With this object in view, I prepare
a few cells that lend themselves to observation. I take a pair of
scissors, slice a piece off the side of the cotton-wool purse, so as
to lay bare both the victuals and the consumer, and place the ripped
cell in a short glass tube. During the first few days, nothing
striking happens. The little grub, with its head still plunged in the
honey, slakes its thirst with long draughts and waxes fat. A moment
comes...But let us go back a little farther, before broaching this
question of sanitation.
Every grub, of whatever kind, fed on provisions collected by the
mother and placed in a narrow cell is subject to conditions of health
unknown to the roving grub that goes where it likes and feeds itself
on what it can pick up. The first, the recluse, is no more able than
the second, the gadabout, to solve the problem of a food which can be
entirely assimilated, without leaving an unclean residue. The second
gives no thought to these sordid matters: any place suits it for
getting rid of that difficulty. But what will the other do with its
waste matter, cooped up as it is in a tiny cell stuffed full of
provisions? A most unpleasant mixture seems inevitable. Picture the
honey-eating grub floating on liquid provisions and fouling them at
intervals with its excretions! The least movement of the hinder-part
would cause the whole to amalgamate; and what a broth that would make
for the delicate nursling! No, it cannot be; those dainty epicures
must have some method of escaping these horrors.
They all have, in fact, and most original methods at that. Some take
the bull by the horns, so to speak, and, in order not to soil things,
refrain from uncleanliness until the end of the meal: they keep the
dropping-trap closed as long as the victuals are unfinished. This is
a radical scheme, but not in every one's power, it appears. It is the
course adopted, for instance, by the Sphex-wasps and the Anthophora-
bees, who, when the whole of the food is consumed, expel at one shot
the residues amassed in the intestines since the commencement of the
repast.
Others, the Osmiae in particular, accept a compromise and begin to
relieve the digestive tract when a suitable space has been made in
the cell through the gradual disappearance of the victuals. Others
again--more hurried these--find means of obeying the common law
pretty early by engaging in stercoral manufactures. By a stroke of
genius, they make the unpleasant obstruction into building-bricks. We
already know the art of the Lily-beetle (Crioceris merdigera. Fabre's
essay on this insect has not yet been translated into English; but
readers interested in the matter will find a full description in "An
Introduction to Entomology," by William Kirby, Rector of Barham, and
William Spence: letter 21.--Translator's Note.), who, with her soft
excrement, makes herself a coat wherein to keep cool in spite of the
sun. It is a very crude and revolting art, disgusting to the eye. The
Diadem Anthidium belongs to another school. With her droppings she
fashions masterpieces of marquetry and mosaic, which wholly conceal
their base origin from the onlooker. Let us watch her labours through
the windows of my tubes.
When the portion of food is nearly half consumed, there begins and
goes on to the end a frequent defecation of yellowish droppings, each
hardly the size of a pin's head. As these are ejected, the grub
pushes them back to the circumference of the cell with a movement of
its hinder-part and keeps them there by means of a few threads of
silk. The work of the spinnerets, therefore, which is deferred in the
others until the provisions are finished, starts earlier here and
alternates with the feeding. In this way, the excretions are kept at
a distance, away from the honey and without any danger of getting
mixed with it. They end by becoming so numerous as to form an almost
continuous screen around the larva. This excremental awning, made
half of silk and half of droppings, is the rough draft of the cocoon,
or rather a sort of scaffolding on which the stones are deposited
until they are definitely placed in position. Pending the piecing
together of the mosaic, the scaffolding keeps the victuals free from
all contamination.
To get rid of what cannot be flung outside, by hanging it on the
ceiling, is not bad to begin with; but to use it for making a work of
art is better still. The honey has disappeared. Now commences the
final weaving of the cocoon. The grub surrounds itself with a wall of
silk, first pure white, then tinted reddish-brown by means of an
adhesive varnish. Through its loose-meshed stuff, it seizes one by
one the droppings hanging from the scaffold and inlays them firmly in
the tissue. The same mode of work is employed by the Bembex-, Stizus-
and Tachytes-wasps and other inlayers, who strengthen the inadequate
woof of their cocoons with grains of sand; only, in their cotton-wool
purses, the Anthidium's grubs substitute for the mineral particles
the only solid materials at their disposal. For them, excrement takes
the place of pebbles.
And the work goes none the worse for it. On the contrary: when the
cocoon is finished, any one who had not witnessed the process of
manufacture would be greatly puzzled to state the nature of the
workmanship. The colouring and the elegant regularity of the outer
wrapper of the cocoon suggest some kind of basket-work made with tiny
bits of bamboo, or a marquetry of exotic granules. I too let myself
be caught by it in my early days and wondered in vain what the hermit
of the cotton wallet had used to inlay her nymphal dwelling so
prettily withal. To-day, when the secret is known to me, I admire the
ingenuity of the insect capable of obtaining the useful and the
beautiful out of the basest materials.
The cocoon has another surprise in store for us. The end containing
the head finishes with a short conical nipple, an apex, pierced by a
narrow shaft that establishes a communication between the inside and
the out. This architectural feature is common to all the Anthidia, to
the resin-workers who will occupy our attention presently, as well as
to the cotton-workers. It is found nowhere outside the Anthidium
group.
What is the use of this point which the larva leaves bare instead of
inlaying it like the rest of the shell? What is the use of that hole,
left quite open or, at most, closed at the bottom with a feeble
grating of silk? The insect appears to attach great importance to it,
from what I see. In point of fact, I watch the careful work of the
apex. The grub, whose movements the hole enables me to follow,
patiently perfects the lower end of the conical channel, polishes it
and gives it an exactly circular shape; from time to time, it inserts
into the passage its two closed mandibles, whose points project a
little way outside; then, opening them to a definite radius, like a
pair of compasses, it widens the aperture and makes it regular.
I imagine, without venturing, however, to make a categorical
statement, that the perforated apex is a chimney to admit the air
required for breathing. Every pupa breathes in its shell, however
compact this may be, even as the unhatched bird breathes inside the
egg. The thousands of pores with which the shell is pierced allow the
inside moisture to evaporate and the outer air to penetrate as and
when needed. The stony caskets of the Bembex- and Stizus-wasps are
endowed, notwithstanding their hardness, with similar means of
exchange between the vitiated and the pure atmosphere. Can the shells
of the Anthidia be air-proof, owing to some modification that escapes
me? In any case, this impermeability cannot be attributed to the
excremental mosaic, which the cocoons of the resin-working Anthidia
do not possess, though endowed with an apex of the very best.
Shall we find an answer to the question in the varnish with which the
silken fabric is impregnated? I hesitate to say yes and I hesitate to
say no, for a host of cocoons are coated with a similar lacquer
though deprived of communication with the outside air. All said,
without being able at present to account for its necessity, I admit
that the apex of the Anthidia is a breathing-aperture. I bequeath to
the future the task of telling us for what reasons the collectors of
both cotton and resin leave a large pore in their shells, whereas all
the other weavers close theirs completely.
After these biological curiosities, it remains for me to discuss the
principal subject of this chapter: the botanical origin of the
materials of the nest. By watching the insect when busy at its
harvesting, or else by examining its manufactured flock under the
microscope, I was able to learn, not without a great expenditure of
time and patience, that the different Anthidia of my neighbourhood
have recourse without distinction to any cottony plant. Most of the
wadding is supplied by the Compositae, particularly the following:
Centaurea solsticialis, or St. Barnaby's thistle; C. paniculata, or
panicled centaury; Echinops ritro, or small globe-thistle; Onopordon
illyricum, or Illyrian cotton-thistle; Helichrysum staechas, or wild
everlasting; Filago germanica, or common cotton-rose. Next come the
Labiatae: Marrubium vulgare, or common white horehound; Ballota
fetida, or stinking horehound; Calamintha nepeta, or lesser calamint;
Salvia aethiopis, or woolly sage. Lastly, the Solanaceae: Verbascum
thapsus, or shepherd's club; V. sinuatum, or scollop-leaved mullein.
The Cotton-bees' flora, we see, incomplete as it is in my notes,
embraces plants of very different aspect. There is no resemblance in
appearance between the proud candelabrum of the cotton-thistle, with
its red tufts, and the humble stalk of the globe-thistle, with its
sky-blue capitula; between the plentiful leaves of the mullein and
the scanty foliage of the St. Barnaby's thistle; between the rich
silvery fleece of the woolly sage and the short hairs of the
everlasting. With the Anthidium, these clumsy botanical
characteristics do not count; one thing alone guides her: the
presence of cotton. Provided that the plant be more or less well-
covered with soft wadding, the rest is immaterial to her.
Another condition, however, has to be fulfilled, apart from the
fineness of the cotton-wool. The plant, to be worth shearing, must be
dead and dry. I have never seen the harvesting done on fresh plants.
In this way, the Bee avoids mildew, which would make its appearance
in a mass of hairs still filled with sap.
Faithful to the plant recognized as yielding good results, the
Anthidium arrives and resumes her gleaning on the edges of the parts
denuded by earlier harvests. Her mandibles scrape away and pass the
tiny fluffs, one by one, to the hind-legs, which hold the pellet
pressed against the chest, mix with it the rapidly-increasing store
of down and make the whole into a little ball. When this is the size
of a pea, it goes back into the mandibles; and the insect flies off,
with its bale of cotton in its mouth. If we have the patience to
wait, we shall see it return to the same point, at intervals of a few
minutes, so long as the bag is not made. The foraging for provisions
will suspend the collecting of cotton; then, next day or the day
after, the scraping will be resumed on the same stalk, on the same
leaf, if the fleece be not exhausted. The owner of a rich crop
appears to keep to it until the closing-plug calls for coarser
materials; and even then this plug is often manufactured with the
same fine flock as the cells.
After ascertaining the diversity of cotton-fields among our native
plants, I naturally had to enquire whether the Cotton-bee would also
put up with exotic plants, unknown to her race; whether the insect
would show any hesitation in the presence of woolly plants offered
for the first time to the rakes of her mandibles. The common clary
and the Babylonian centaury, with which I have stocked the harmas,
shall be the harvest-fields; the reaper shall be the Diadem
Anthidium, the inmate of my reeds.
The common clary, or toute-bonne, forms part, I know, of our French
flora to-day; but it is an acclimatized foreigner. They say that a
gallant crusader, returning from Palestine with his share of glory
and bruises, brought back the toute-bonne from the Levant to help him
cure his rheumatism and dress his wounds. From the lordly manor, the
plant propagated itself in all directions, while remaining faithful
to the walls under whose shelter the noble dames of yore used to grow
it for their unguents. To this day, feudal ruins are its favourite
resorts. Crusaders and manors disappeared; the plant remained. In
this case, the origin of the clary, whether historical or legendary,
is of secondary importance. Even if it were of spontaneous growth in
certain parts of France, the toute-bonne is undoubtedly a stranger in
the Vaucluse district. Only once in the course of my long botanizing-
expeditions across the department have I come upon this plant. It was
at Caromb, in some ruins, nearly thirty years ago. I took a cutting
of it; and since then the crusaders' sage has accompanied me on all
my peregrinations. My present hermitage possesses several tufts of
it: but, outside the enclosure, except at the foot of the walls, it
would be impossible to find one. We have, therefore, a plant that is
new to the country for many miles around, a cotton-field which the
Serignan Cotton-bees had never utilized before I came and sowed it.
Nor had they ever made use of the Babylonian centaury, which I was
the first to introduce in order to cover my ungrateful stony soil
with some little vegetation. They had never seen anything like the
colossal centaury imported from the region of the Euphrates. Nothing
in the local flora, not even the cotton-thistle, had prepared them
for this stalk as thick as a child's wrist, crowned at a height of
nine feet with a multitude of yellow balls, nor for those great
leaves spreading over the ground in an enormous rosette. What will
they do in the presence of such a find? They will take possession of
it with no more hesitation than if it were the humble St. Barnaby's
thistle, the usual purveyor.
In fact, I place a few stalks of clary and Babylonian centaury, duly
dried, near the reed-hives. The Diadem Anthidium is not long in
discovering the rich harvest. Straight away the wool is recognized as
being of excellent quality, so much so that, during the three or four
weeks of nest-building, I can daily witness the gleaning, now on the
clary, now on the centaury. Nevertheless the Babylonian plant appears
to be preferred, no doubt because of its whiter, finer and more
plentiful down. I keep a watchful eye on the scraping of the
mandibles and the work of the legs as they prepare the pellet; and I
see nothing that differs from the operations of the insect when
gleaning on the globe-thistle and the St. Barnaby's thistle. The
plant from the Euphrates and the plant from Palestine are treated
like those of the district.
Thus we find what the Leaf-cutters taught us proved, in another way,
by the cotton-gatherers. In the local flora, the insect has no
precise domain; it reaps its harvest readily now from one species,
now from another, provided that it find the materials for its
manufactures. The exotic plant is accepted quite as easily as that of
indigenous growth. Lastly, the change from one plant to another, from
the common to the rare, from the habitual to the exceptional, from
the known to the unknown, is made suddenly, without gradual
initiations. There is no novitiate, no training by habit in the
choice of the materials for the nest. The insect's industry, variable
in its details by sudden, individual and non-transmissible
innovations, gives the lie to the two great factors of evolution:
time and heredity.
CHAPTER 10. THE RESIN-BEES.
At the time when Fabricius (Johann Christian Fabricius (1745-1808), a
noted Danish entomologist, author of "Systema entomologiae" (1775).--
Translator's Note.) gave the genus Anthidium its name, a name still
used in our classifications, entomologists troubled very little about
the live animal; they worked on corpses, a dissecting-room method
which does not yet seem to be drawing to an end. They would examine
with a conscientious eye the antenna, the mandible, the wing, the
leg, without asking themselves what use the insect had made of those
organs in the exercise of its calling. The animal was classified very
nearly after the manner adopted in crystallography. Structure was
everything; life, with its highest prerogatives, intellect, instinct,
did not count, was not worthy of admission into the zoological
scheme.
It is true that an almost exclusively necrological study is
obligatory at first. To fill one's boxes with insects stuck on pins
is an operation within the reach of all; to watch those same insects
in their mode of life, their work, their habits and customs is quite
a different thing. The nomenclator who lacks the time--and sometimes
also the inclination--takes his magnifying-glass, analyzes the dead
body and names the worker without knowing its work. Hence the number
of appellations the least of whose faults is that they are unpleasant
to the ear, certain of them, indeed, being gross misnomers. Have we
not, for instance, seen the name of Lithurgus, or stone-worker, given
to a Bee who works in wood and nothing but wood? Such absurdities
will be inevitable until the animal's profession is sufficiently
familiar to lend its aid in the compiling of diagnoses. I trust that
the future will see this magnificent advance in entomological
science: men will reflect that the impaled specimens in our
collections once lived and followed a trade; and anatomy will be kept
in its proper place and made to leave due room for biology.
Fabricius did not commit himself with his expression Anthidium, which
alludes to the love of flowers, but neither did he mention anything
characteristic: as all Bees have the same passion in a very high
degree, I see no reason to treat the Anthidia as more zealous looters
than the others. If he had known their cotton nests, perhaps the
Scandinavian naturalist would have given them a more logical
denomination. As for me, in a language wherein technical parade is
out of place, I will call them the Cotton-bees.
The term requires some limiting. To judge by my finds, in fact, the
old genus Anthidium, that of the classifying entomologists, comprises
in my district two very different corporations. One is known to us
and works exclusively in wadding; the other, which we are about to
study, works in resin, without ever having recourse to cotton.
Faithful to my extremely simple principle of defining the worker, as
far as possible, by his work, I will call the members of this guild
the Resin-bees. Thus confining myself to the data supplied by my
observations, I divide the Anthidium group into equal sections, of
equal importance, for which I demand special generic titles; for it
is highly illogical to call the carders of wool and the kneaders of
resin by the same name. I surrender to those whom it concerns the
honour of effecting this reform in the orthodox fashion.
Good luck, the friend of the persevering, made me acquainted in
different parts of Vaucluse with four Resin-bees whose singular trade
no one had yet suspected. To-day, I find them all four again in my
own neighbourhood. They are the following: Anthidium septemdentatum,
LATR., A. bellicosum, LEP., A. quadrilobum, LEP., and A. Latreillii,
LEP. The first two make their nests in deserted Snail-shells; the
other two shelter their groups of cells sometimes in the ground,
sometimes under a large stone. We will first discuss the inhabitants
of the Snail-shell. I made a brief reference to them in an earlier
chapter, when speaking of the distribution of the sexes. This mere
allusion, suggested by a study of a different kind, must now be
amplified. I return to it with fuller particulars.
The stone-heaps in the Roman quarries near Serignan, which I have so
often visited in search of the nests of the Osmia who takes up her
abode in Snail-shells, supply me also with the two Resin-bees
installed in similar quarters. When the Field-mouse has left behind
him a rich collection of empty shells scattered all round his hay
mattress under the slab, there is always a hope of finding some
Snail-shells plugged with mud and, here and there, mixed with them, a
few Snail-shells closed with resin. The two Bees work next door to
each other, one using clay, the other gum. The excellence of the
locality is responsible for this frequent cohabitation, shelter being
provided by the broken stone from the quarry and lodgings by the
shells which the Mouse has left behind.
At places where dead Snail-shells are few and far between, as in the
crevices of rustic walls, each Bee occupies by herself the shells
which she has found. But here, in the quarries, our crop will
certainly be a double or even a treble one, for both Resin-bees
frequent the same heaps. Let us, therefore, lift the stones and dig
into the mound until the excessive dampness of the subsoil tells us
that it is useless to look lower down. Sometimes at the moment of
removing the first layer, sometimes at a depth of eighteen inches, we
shall find the Osmia's Snail-shell and, much more rarely, the Resin-
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