Bramble-bees and Others
by
J. Henri Fabre
Part 2 out of 5
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These examples are more than sufficient. It is quite evident that the
distribution of the sexes is not governed by any rule. All that I can
say on consulting the whole of my notes, which contain a good many
instances of complete layings--most of them, unfortunately, spoilt
through gaps caused by parasites, the death of the larva, the failure
of the egg to hatch and other accidents--all that I can say in
general is that the complete series begins with females and nearly
always ends with males. The incomplete series can teach us nothing in
this respect, for they are only fragments starting we know not
whence; and it is impossible to tell whether they should be ascribed
to the beginning, to the end, or to an intermediate period of the
laying. To sum up: in the laying of the Three-pronged Osmia, no order
governs the succession of the sexes; only, the series has a marked
tendency to begin with females and to finish with males.
The brambles, in my district, harbour two other Osmiae, both of much
smaller size: O. detrita, PEREZ, and O. parvula, DUF. The first is
very common, the second very rare; and until now I have found only
one of her nests, placed above a nest of O. detrita, in the same
bramble. Here, instead of the lack of order in the distribution of
the sexes which we find with O. tridentata, we have an order
remarkable for consistency and simplicity. I have before me the list
of the series of O. detrita collected last winter. Here are some of
them:
1. A series of twelve: seven females, beginning with the bottom of
the tunnel, and then five males.
2. A series of nine: three females first, then six males.
3. A series of eight: five females followed by three males.
4. A series of eight: seven females followed by one male.
5. A series of eight: one female followed by seven males.
6. A series of seven: six females followed by one male.
The first series might very well be complete. The second and fifth
appear to be the end of layings, of which the beginning has taken
place elsewhere, in another bramble-stump. The males predominate and
finish off the series. Nos. 3, 4 and 6, on the other hand, look like
the beginnings of layings: the females predominate and are at the
head of the series. Even if these interpretations should be open to
doubt, one result at least is certain: with O. detrita, the laying is
divided into two groups, with no intermingling of the sexes; the
first group laid yields nothing but females, the second, or more
recent, yields nothing but males.
What was only a sort of attempt with the Three-pronged Osmia--who, it
is true, begins with females and ends with males, but muddles up the
order and mixes the two sexes anyhow between the extreme points--
becomes a regular law with her kinswoman. The mother occupies herself
at the start with the stronger sex, the more necessary, the better-
gifted, the female sex, to which she devotes the first flush of her
laying and the fullness of her vigour; later, when she is perhaps
already at the end of her strength, she bestows what remains of her
maternal solicitude upon the weaker sex, the less-gifted, almost
negligible male sex.
O. parvula, of whom I unfortunately possess but one series, repeats
what the previous witness has just shown us. This series, one of nine
cocoons, comprises five females followed by four males, without any
mixing of the sexes.
Next to these disgorgers of honey and gleaners of pollen-dust, it
would be well to consult other Hymenoptera, Wasps who devote
themselves to the chase and pile their cells one after the other, in
a row, showing the relative age of the cocoons. The brambles house
several of these: Solenius vagus, who stores up Flies; Psen atratus,
who provides her grubs with a heap of Plant-lice; Trypoxylon figulus,
who feeds them with Spiders.
Solenius vagus digs her gallery in a bramble-stick that is lopped
short, but still fresh and green. The house of this Fly-huntress,
therefore, suffers from damp, as the sap enters, especially on the
lower floors. This seems to me rather insanitary. To avoid the
humidity, or for other reasons which escape me, the Solenius does not
dig very far into her bramble-stump and consequently can stack but a
small number of cells in it. A series of five cocoons gives me first
four females and then one male; another series, also of five,
contains first three females, with two males following. These are the
most complete that I have for the moment.
I reckoned on the Black Psen, or Psen atratus, whose series are
pretty long; it is a pity that they are nearly always greatly
interfered with by a parasite called Ephialtes mediator. (Cf. "The
Life of the Fly": chapter 2.--Translator's Note.) I obtained only
three series free from gaps: one of eight cocoons, comprising only
females; one of six, likewise consisting wholly of females; lastly,
one of eight, formed exclusively of males. These instances seem to
show that the Psen arranges her laying in a succession of females and
a succession of males; but they tell us nothing of the relative order
of the two series.
>From the Spider-huntress, Trypoxylon figulus, I learnt nothing
decisive. She appeared to me to rove about from one bramble to the
next, utilizing galleries which she has not dug herself. Not
troubling to be economical with a lodging which it has cost her
nothing to acquire, she carelessly builds a few partitions at very
unequal heights, stuffs three or four compartments with Spiders and
passes on to another bramble-stump, with no reason, so far as I know,
for abandoning the first. Her cells, therefore, occur in series that
are too short to give us any useful information.
This is all that the bramble-dwellers have to tell us; I have
enumerated the list of the principal ones in my district. We will now
look into some other Bees who arrange their cocoons in single files:
the Megachiles (Cf. Chapter 8 of the present volume.--Translator's
Note.), who cut disks out of leaves and fashion the disks into
thimble-shaped receptacles; the Anthidia (Cf. Chapters 9 and 10 of
the present volume.--Translator's Note.), who weave their honey-
wallets out of cotton-wool and arrange their cells one after the
other in some cylindrical gallery. In most cases, the home is the
produce of neither the one nor the other. A tunnel in the upright,
earthy banks, the old work of some Anthophora, is the usual dwelling.
There is no great depth to these retreats; and all my searches,
zealously prosecuted during a number of winters, procured me only
series containing a small number of cocoons, four or five at most,
often one alone. And, what is quite as serious, nearly all these
series are spoilt by parasites and allow me to draw no well-founded
deductions.
I remembered finding, at rare intervals, nests of both the Anthidium
and the Megachile in the hollows of cut reeds. I thereupon installed
some hives of a new kind on the sunniest walls of my enclosure. They
consisted of stumps of the great reed of the south, open at one end,
closed at the other by the natural knot and gathered into a sort of
enormous pan-pipe, such as Polyphemus might have employed. The
invitation was accepted: Osmiae, Anthidia and Megachiles came in
fairly large numbers, especially the first, to benefit by the queer
installation.
In this way I obtained some magnificent series of Anthidia and
Megachiles, running up to a dozen. There was a melancholy side to
this success. All my series, with not one exception, were ravaged by
parasites. Those of the Megachile (M. sericans, FONSCOL), who
fashions her goblets with robinia-, holm-, and terebinth-leaves, were
inhabited by Coelioxys octodentata (A Parasitic Bee.--Translator's
Note.); those of the Anthidium (A. florentinum, LATR.) were occupied
by a Leucopsis. Both kinds were swarming with a colony of pigmy
parasites whose name I have not yet been able to discover. In short,
my pan-pipe hives, though very useful to me from other points of
view, taught me nothing about the order of the sexes among the Leaf-
cutters and the cotton-weavers.
I was more fortunate with three Osmiae (O. tricornis, LATR., O.
cornuta, LATR., and O. Latreillii, SPIN.), all of whom gave me
splendid results, with reed-stumps arranged either against the walls
of my garden, as I have just said, or near their customary abode, the
huge nests of the Mason-bee of the Sheds. One of them, the Three-
horned Osmia, did better still: as I have described, she built her
nests in my study, as plentifully as I could wish, using reeds, glass
tubes and other retreats of my selecting for her galleries.
We will consult this last, who has furnished me with documents beyond
my fondest hopes, and begin by asking her of how many eggs her
average laying consists. Of the whole heap of colonized tubes in my
study, or else out of doors, in the hurdle-reeds and the pan-pipe
appliances, the best-filled contains fifteen cells, with a free space
above the series, a space showing that the laying is ended, for, if
the mother had any more eggs available, she would have lodged them in
the room which she leaves unoccupied. This string of fifteen appears
to be rare; it was the only one that I found. My attempts at indoor
rearing, pursued during two years with glass tubes or reeds, taught
me that the Three-horned Osmia is not much addicted to long series.
As though to decrease the difficulties of the coming deliverance, she
prefers short galleries, in which only a part of the laying is
stacked. We must then follow the same mother in her migration from
one dwelling to the next if we would obtain a complete census of her
family. A spot of colour, dropped on the Bee's thorax with a paint-
brush while she is absorbed in closing up the mouth of the tunnel,
enables us to recognize the Osmia in her various homes.
In this way, the swarm that resided in my study furnished me, in the
first year, with an average of twelve cells. Next year, the summer
appeared to be more favourable and the average became rather higher,
reaching fifteen. The most numerous laying performed under my eyes,
not in a tube, but in a succession of Snail-shells, reached the
figure of twenty-six. On the other hand, layings of between eight and
ten are not uncommon. Lastly, taking all my records together, the
result is that the family of the Osmia fluctuates round about fifteen
in number.
I have already spoken of the great differences in size apparent in
the cells of one and the same series. The partitions, at first widely
spaced, draw gradually nearer to one another as they come closer to
the aperture, which implies roomy cells at the back and narrow cells
in front. The contents of these compartments are no less uneven
between one portion and another of the string. Without any exception
known to me, the large cells, those with which the series starts,
have more abundant provisions than the straitened cells with which
the series ends. The heap of honey and pollen in the first is twice
or even thrice as large as that in the second. In the last cells, the
most recent in date, the victuals are but a pinch of pollen, so
niggardly in amount that we wonder what will become of the larva with
that meagre ration.
One would think that the Osmia, when nearing the end of the laying,
attaches no importance to her last-born, to whom she doles out space
and food so sparingly. The first-born receive the benefit of her
early enthusiasm: theirs is the well-spread table, theirs the
spacious apartments. The work has begun to pall by the time that the
last eggs are laid; and the last-comers have to put up with a scurvy
portion of food and a tiny corner.
The difference shows itself in another way after the cocoons are
spun. The large cells, those at the back, receive the bulky cocoons;
the small ones, those in front, have cocoons only a half or a third
as big. Before opening them and ascertaining the sex of the Osmia
inside, let us wait for the transformation into the perfect insect,
which will take place towards the end of summer. If impatience gets
the better of us, we can open them at the end of July or in August.
The insect is then in the nymphal stage; and it is easy, under this
form, to distinguish the two sexes by the length of the antennae,
which are larger in the males, and by the glassy protuberances on the
forehead, the sign of the future armour of the females. Well, the
small cocoons, those in the narrow front cells, with their scanty
store of provisions, all belong to males; the big cocoons, those in
the spacious and well-stocked cells at the back, all belong to
females.
The conclusion is definite: the laying of the Three-horned Osmia
consists of two distinct groups, first a group of females and then a
group of males.
With my pan-pipe apparatus displayed on the walls of my enclosure and
with old hurdle-reeds left lying flat out of doors, I obtained the
Horned Osmia in fair quantities. I persuaded Latreille's Osmia to
build her nest in reeds, which she did with a zeal which I was far
from expecting. All that I had to do was to lay some reed-stumps
horizontally within her reach, in the immediate neighbourhood of her
usual haunts, namely, the nests of the Mason-bee of the Sheds.
Lastly, I succeeded without difficulty in making her build her nests
in the privacy of my study, with glass tubes for a house. The result
surpassed my hopes.
With both these Osmiae, the division of the gallery is the same as
with the Three-horned Osmia. At the back are large cells with
plentiful provisions and widely-spaced partitions; in front, small
cells, with scanty provisions and partitions close together. Also,
the larger cells supplied me with big cocoons and females; the
smaller cells gave me little cocoons and males. The conclusion
therefore is exactly the same in the case of all three Osmiae.
Before dismissing the Osmiae, let us devote a moment to their
cocoons, a comparison of which, in the matter of bulk, will furnish
us with fairly accurate evidence as to the relative size of the two
sexes, for the thing contained, the perfect insect, is evidently
proportionate to the silken wrapper in which it is enclosed. These
cocoons are oval-shaped and may be regarded as ellipsoids formed by a
revolution around the major axis. The volume of one of these solids
is expressed in the following formula:
4 / 3 x pi x a x (b squared),
in which 2a is the major axis and 2b the minor axis.
Now, the average dimensions of the cocoons of the Three-horned Osmia
are as follows:
2a = 13 mm. (.507 inch.--Translator's Note.), 2b = 7 mm. (.273 inch.-
-Translator's Note.) in the females;
2a = 9 mm. (.351 inch.--Translator's Note.), 2b = 5 mm. (.195 inch.--
Translator's Note.) in the males.
The ratio therefore between 13 x 7 x 7 = 637 and 9 x 5 x 5 = 225 will
be more or less the ratio between the sizes of the two sexes. This
ratio is somewhere between 2 to 1 and 3 to 1. The females therefore
are two or three times larger than the males, a proportion already
suggested by a comparison of the mass of provisions, estimated simply
by the eye.
The Horned Osmia gives us the following average dimensions:
2a = 15 mm. (.585 inch.--Translator's Note.), 2b = 9 mm. (.351 inch.-
-Translator's Note.) in the females;
2a = 12 mm. (.468 inch.--Translator's Note.), 2b = 7 mm. (.273 inch.-
-Translator's Note.) in the males.
Once again, the ratio between 15 x 9 x 9 = 1215 and 12 x 7 x 7 = 588
lies between 2 to 1 and 3 to 1.
Besides the Bees who arrange their laying in a row, I have consulted
others whose cells are grouped in a way that makes it possible to
ascertain the relative order of the two sexes, though not quite so
precisely. One of these is the Mason-bee of the Walls. I need not
describe again her dome-shaped nest, built on a pebble, which is now
so well-known to us. (Cf. "The Mason-bees": chapter 1.--Translator's
Note.)
Each mother chooses her stone and works on it in solitude. She is an
ungracious landowner and guards her site jealously, driving away any
Mason who even looks as though she might alight on it. The
inhabitants of the same nest are therefore always brothers and
sisters; they are the family of one mother.
Moreover, if the stone presents a large enough surface--a condition
easily fulfilled--the Mason-bee has no reason to leave the support on
which she began her laying and go in search of another whereon to
deposit the rest of her eggs. She is too thrifty of her time and of
her mortar to involve herself in such expenditure except for grave
reasons. Consequently, each nest, at least when it is new, when the
Bee herself has laid the first foundations, contains the entire
laying. It is a different thing when an old nest is restored and made
into a place for depositing the eggs. I shall come back later to such
houses.
A newly-built nest then, with rare exceptions, contains the entire
laying of one female. Count the cells and we shall have the total
list of the family. Their maximum number fluctuates round about
fifteen. The most luxuriant series will occasionally reach as many as
eighteen, though these are very scarce.
When the surface of the stone is regular all around the site of the
first cell, when the mason can add to her building with the same
facility in every direction, it is obvious that the groups of cells,
when finished, will have the oldest in the central portion and the
more recent in the surrounding portion. Because of this juxtaposition
of the cells, which serve partly as a wall to those which come next,
it is possible to form some estimate of the chronological order of
the cells in the Chalicodoma's nest and thus to discover the sequence
of the two sexes.
In winter, by which time the Bee has long been in the perfect state,
I collect Chalicodoma-nests, removing them bodily from their support
with a few smart sideward taps of the hammer on the pebbles. At the
base of the mortar dome the cells are wide agape and display their
contents. I take the cocoon from its box, open it and take note of
the sex of the insect enclosed.
I should probably be accused of exaggeration if I mentioned the total
number of the nests which I have gathered and the cells which I have
inspected by this method during the last six or seven years. I will
content myself with saying that the harvest of a single morning
sometimes consisted of as many as sixty nests of the Mason-bee. I had
to have help in carrying home my spoils, even though the nests were
removed from their stones on the spot.
>From the enormous number of nests which I have examined, I am able to
state that, when the cluster is regular, the female cells occupy the
centre and the male cells the edges. Where the irregularity of the
pebble has prevented an even distribution around the initial point,
the same rule has been observed. A male cell is never surrounded on
every side by female cells: either it occupies the edges of the nest,
or else it adjoins, at least on some sides, other male cells, of
which the last form part of the exterior of the cluster. As the
surrounding cells are obviously of a later date than the inner cells,
it follows that the Mason-bee acts like the Osmiae: she begins her
laying with females and ends it with males, each of the sexes forming
a series of its own, independent of the other.
Some further circumstances add their testimony to that of the
surrounded and surrounding cells. When the pebble projects sharply
and forms a sort of dihedral angle, one of whose faces is more or
less vertical and the other horizontal, this angle is a favourite
site with the Mason, who thus finds greater stability for her edifice
in the support given her by the double plane. These sites appear to
me to be in great request with the Chalicodoma, considering the
number of nests which I find thus doubly supported. In nests of this
kind, all the cells, as usual, have their foundations fixed to the
horizontal surface; but the first row, the row of cells first built,
stands with its back against the vertical surface.
Well, these older cells, which occupy the actual edge of the dihedral
angle, are always female, with the exception of those at either end
of the row, which, as they belong to the outside, may be male cells.
In front of this first row come others. The female cells occupy the
middle portion and the male the ends. Finally, the last row, closing
in the remainder, contains only male cells. The progress of the work
is very visible here: the Mason has begun by attending to the central
group of female cells, the first row of which occupies the dihedral
angle, and has finished her task by distributing the male cells round
the outside.
If the perpendicular face of the dihedral angle be high enough, it
sometimes happens that a second row of cells is placed above the
first row backing on to that plane; a third row occurs less often.
The nest is then one of several storeys. The lower storeys, the
older, contain only females; the upper, the more recent storey,
contains none but males. It goes without saying that the surface
layer, even of the lower storeys, can contain males without
invalidating the rule, for this layer may always be looked upon as
the Chalicodoma's last work.
Everything therefore contributes to show that, in the Mason-bee, the
females take the lead in the order of primogeniture. Theirs is the
central and best-protected part of the clay fortress; the outer part,
that most exposed to the inclemencies of the weather and to
accidents, is for the males.
The males' cells do not differ from the females' only by being placed
at the outside of the cluster; they differ also in their capacity,
which is much smaller. To estimate the respective capacities of the
two sorts of cells, I go to work as follows: I fill the empty cell
with very fine sand and pour this sand back into a glass tube
measuring 5 millimetres (.195 inch.--Translator's Note.) in diameter.
>From the height of the column of sand we can estimate the comparative
capacity of the two kinds of cells. I will take one at random among
my numerous examples of cells thus gauged.
It comprises thirteen cells and occupies a dihedral angle. The female
cells give me the following figures, in millimetres, as the height of
the columns of sand:
40, 44, 43, 48, 48, 46, 47
(1.56, 1.71, 1.67, 1.87, 1.87, 1.79, 1.83 inches.--Translator's
Note.),
averaging 45. (1.75 inches.--Translator's Note.)
The male cells give me:
32, 35, 28, 30, 30, 31
(1.24, 1.36, 1.09, 1.17, 1.17, 1.21 inches.--Translator's Note.),
averaging 31. (1.21 inches.--Translator's Note.)
The ratio of the capacity of the cells for the two sexes is therefore
roughly a ratio of 4 to 3. The actual contents of the cell being
proportionate to its capacity, the above ratio must also be more or
less the ratio of provisions and sizes between females and males.
These figures will assist us presently to tell whether an old cell,
occupied for a second or third time, belonged originally to a female
or a male.
The Chalicodoma of the Sheds cannot give us any information on this
matter. She builds under the same eaves, in excessively populous
colonies; and it is impossible to follow the labours of any single
Mason, whose cells, distributed here and there, are soon covered up
with the work of her neighbours. All is muddle and confusion in the
individual output of the swarming throng.
I have not watched the work of the Chalicodoma of the Shrubs with
close enough attention to be able to state definitely that this Bee
is a solitary builder. Her nest is a ball of clay hanging from a
bough. Sometimes, this nest is the size of a large walnut and then
appears to be the work of one alone; sometimes, it is the size of a
man's fist, in which case I have no doubt that it is the work of
several. Those bulky nests, comprising more than fifty cells, can
tell us nothing exact, as a number of workers must certainly have
collaborated to produce them.
The walnut-sized nests are more trustworthy, for everything seems to
indicate that they were built by a single Bee. Here females are found
in the centre of the group and males at the circumference, in
somewhat smaller cells, thus repeating what the Mason-bee of the
Pebbles has told us.
One clear and simple rule stands out from this collection of facts.
Apart from the strange exception of the Three-pronged Osmia, who
mixes the sexes without any order, the Bees whom I studied and
probably a crowd of others produce first a continuous series of
females and then a continuous series of males, the latter with less
provisions and smaller cells. This distribution of the sexes agrees
with what we have long known of the Hive-bee, who begins her laying
with a long sequence of workers, or sterile females, and ends it with
a long sequence of males. The analogy continues down to the capacity
of the cells and the quantities of provisions. The real females, the
Queen-bees, have wax cells incomparably more spacious than the cells
of the males and receive a much larger amount of food. Everything
therefore demonstrates that we are here in the presence of a general
rule.
But does this rule express the whole truth? Is there nothing beyond a
laying in two series? Are the Osmiae, the Chalicodomae and the rest
of them fatally bound by this distribution of the sexes into two
distinct groups, the male group following upon the female group,
without any mixing of the two? Is the mother absolutely powerless to
make a change in this arrangement, should circumstances require it?
The Three-pronged Osmia already shows us that the problem is far from
being solved. In the same bramble-stump, the two sexes occur very
irregularly, as though at random. Why this mixture in the series of
cocoons of a Bee closely related to the Horned Osmia and the Three-
horned Osmia, who stack theirs methodically by separate sexes in the
hollow of a reed? What the Bee of the brambles does cannot her
kinswomen of the reeds do too? Nothing, so far as I know, can explain
this difference in a physiological act of primary importance. The
three Bees belong to the same genus; they resemble one another in
general outline, internal structure and habits; and, with this close
similarity, we suddenly find a strange dissimilarity.
There is just one thing that might possibly arouse a suspicion of the
cause of this irregularity in the Three-pronged Osmia's laying. If I
open a bramble-stump in the winter to examine the Osmia's nest, I
find it impossible, in the vast majority of cases, to distinguish
positively between a female and a male cocoon: the difference in size
is so small. The cells, moreover, have the same capacity: the
diameter of the cylinder is the same throughout and the partitions
are almost always the same distance apart. If I open it in July, the
victualling-period, it is impossible for me to distinguish between
the provisions destined for the males and those destined for the
females. The measurement of the column of honey gives practically the
same depth in all the cells. We find an equal quantity of space and
food for both sexes.
This result makes us foresee what a direct examination of the two
sexes in the adult form tells us. The male does not differ materially
from the female in respect of size. If he is a trifle smaller, it is
scarcely noticeable, whereas, in the Horned Osmia and the Three-
horned Osmia, the male is only half or a third the size of the
female, as we have seen from the respective bulk of their cocoons. In
the Mason-bee of the Walls there is also a difference in size, though
less pronounced.
The Three-pronged Osmia has not therefore to trouble about adjusting
the dimensions of the dwelling and the quantity of the food to the
sex of the egg which she is about to lay; the measure is the same
from one end of the series to the other. It does not matter if the
sexes alternate without order: one and all will find what they need,
whatever their position in the row. The two other Osmiae, with their
great disparity in size between the two sexes, have to be careful
about the twofold consideration of board and lodging. And that, I
think, is why they begin with spacious cells and generous rations for
the homes of the females and end with narrow, scantily-provisioned
cells, the homes of the males. With this sequence, sharply defined
for the two sexes, there is less fear of mistakes which might give to
one what belongs to another. If this is not the explanation of the
facts, I see no other.
The more I thought about this curious question, the more probable it
appeared to me that the irregular series of the Three-pronged Osmia
and the regular series of the other Osmiae, of the Chalicodomae and
of the Bees in general were all traceable to a common law. It seemed
to me that the arrangement in a succession first of females and then
of males did not account for everything. There must be something
more. And I was right: that arrangement in series is only a tiny
fraction of the reality, which is remarkable in a very different way.
This is what I am going to prove by experiment.
CHAPTER 4. THE MOTHER DECIDES THE SEX OF THE EGG.
I will begin with the Mason-bee of the Pebbles. (This is the same
insect as the Mason-bee of the Walls. Cf. "The Mason-bees": passim.--
Translator's Note.) The old nests are often used, when they are in
good enough repair. Early in the season the mothers quarrel fiercely
over them; and, when one of the Bees has taken possession of the
coveted dome, she drives any stranger away from it. The old house is
far from being a ruin, only it is perforated with as many holes as it
once had occupants. The work of restoration is no great matter. The
heap of earth due to the destruction of the lid by the outgoing
tenant is taken out of the cell and flung away at a distance, atom by
atom. The remnants of the cocoon are also thrown away, but not
always, for the delicate silken wrapper sometimes adheres closely to
the masonry.
The victualling of the renovated cell is now begun. Next comes the
laying; and lastly the orifice is sealed with a mortar plug. A second
cell is utilized in the same way, followed by a third and so on, one
after the other, as long as any remain unoccupied and the mother's
ovaries are not exhausted. Finally, the dome receives, mainly over
the apertures already plugged, a coat of plaster which makes the nest
look like new. If she has not finished her laying, the mother goes in
search of other old nests to complete it. Perhaps she does not decide
to found a new establishment except when she can find no second-hand
dwellings, which mean a great economy of time and labour. In short,
among the countless number of nests which I have collected, I find
many more ancient than recent ones.
How shall we distinguish one from the other? The outward aspect tells
you nothing, owing to the great care taken by the Mason to restore
the surface of the old dwelling equal to new. To resist the rigours
of the winter, this surface must be impregnable. The mother knows
that and therefore repairs the dome. Inside, it is another matter:
the old nest stands revealed at once. There are cells whose
provisions, at least a year old, are intact, but dried up or musty,
because the egg has never developed. There are others containing a
dead larva, reduced by time to a blackened, curled-up cylinder. There
are some whence the perfect insect was never able to issue: the
Chalicodoma wore herself out in trying to pierce the ceiling of her
chamber; her strength failed her and she perished in the attempt.
Others again and very many are occupied by ravagers, Leucopses (Cf.
"The Mason-bees": chapter 11.--Translator's Note.) and Anthrax-flies,
who will come out a good deal later, in July. Altogether, the house
is far from having every room vacant; there are nearly always a
considerable number occupied either by parasites that were still in
the egg-stage at the time when the Mason-bee was at work or by
damaged provisions, dried grubs or Chalicodomae in the perfect state
who have died without being able to effect their deliverance.
Should all the rooms be available, a rare occurrence, there still
remains a method of distinguishing between an ancient nest and a
recent one. The cocoon, as I have said, adheres pretty closely to the
walls; and the mother does not always take away this remnant, either
because she is unable to do so, or because she considers the removal
unnecessary. Thus the base of the new cocoon is set in the bottom of
the old cocoon. This double wrapper points very clearly to two
generations, two separate years. I have even found as many as three
cocoons fitting one into another at their bases. Consequently, the
nests of the Mason-bee of the Pebbles are able to do duty for three
years, if not more. Eventually they become utter ruins, abandoned to
the Spiders and to various smaller Bees or Wasps, who take up their
quarters in the crumbling rooms.
As we see, an old nest is hardly ever capable of containing the
Mason-bee's entire laying, which calls for some fifteen apartments.
The number of rooms at her disposal is most unequal, but always very
small. It is saying much when there are enough to receive about half
the laying. Four or five cells, sometimes two or even one: that is
what the Mason usually finds in a nest that is not her own work. This
large reduction is explained when we remember the numerous parasites
that live upon the unfortunate Bee.
Now, how are the sexes distributed in those layings which are
necessarily broken up between one old nest and another? They are
distributed in such a way as utterly to upset the idea of an
invariable succession first of females and then of males, the idea
which occurs to us on examining the new nests. If this rule were a
constant one, we should be bound to find in the old domes at one time
only females, at another only males, according as the laying was at
its first or at its second stage. The simultaneous presence of the
two sexes would then correspond with the transition period between
one stage and the next and should be very unusual. On the contrary,
it is very common; and, however few cells there may be, we always
find both females and males in the old nests, on the sole condition
that the compartments have the regulation holding-capacity, a large
capacity for the females, a lesser for the males, as we have seen.
The old male cells can be recognized by their position on the outer
edges and by their capacity, measuring on an average the same as a
column of sand 31 millimetres high in a glass tube 5 millimetres
wide. (1.21 x .195 inches.--Translator's Note.) These cells contain
males of the second or third generation and none but males. In the
old female cells, those in the middle, whose capacity is measured by
a similar column of sand 45 millimetres high (1.75 inches.--
Translator's Note.), are females and none but females.
This presence of both sexes at a time, even when there are but two
cells free, one spacious and the other small, proves in the plainest
fashion that the regular distribution observed in the complete nests
of recent production is here replaced by an irregular distribution,
harmonizing with the number and holding-capacity of the chambers to
be stocked. The Mason-bee has before her, let me suppose, only five
vacant cells: two larger and three smaller. The total space at her
disposal would do for about a third of the laying. Well, in the two
large cells, she puts females; in the three small cells, she puts
males.
As we find the same sort of thing in all the old nests, we must needs
admit that the mother knows the sex of the egg which she is going to
lay, because that egg is placed in a cell of the proper capacity. We
can go further and admit that the mother alters the order of
succession of the sexes at her pleasure, because her layings, between
one old nest and another, are broken up into small groups of males
and females according to the exigencies of space in the actual nest
which she happens to be occupying.
Just now, in the new nest, we saw the Mason-bee arranging her total
laying into series first of females and next of males; and here she
is, mistress of an old nest of which she has not the power to alter
the arrangement, breaking up her laying into sections comprising both
sexes just as required by the conditions imposed upon her. She
therefore decides the sex of the egg at will, for, without this
prerogative, she could not, in the chambers of the nest which she
owes to chance, deposit unerringly the sex for which those chambers
were originally built; and this happens however small the number of
chambers to be filled.
When the nest is new, I think I see a reason why the Mason-bee should
seriate her laying into females and then males. Her nest is a half-
sphere. That of the Mason-bee of the Shrubs is very nearly a sphere.
Of all shapes, the spherical shape is the strongest. Now these two
nests require an exceptional power of resistance. Without protection
of any kind, they have to brave the weather, one on its pebble, the
other on its bough. Their spherical configuration is therefore very
practical.
The nest of the Mason-bee of the Walls consists of a cluster of
upright cells backing against one another. For the whole to take a
spherical form, the height of the chambers must diminish from the
centre of the dome to the circumference. Their elevation is the sine
of the meridian arc starting from the plane of the pebble. Therefore,
if they are to have any solidity, there must be large cells in the
middle and small cells at the edges. And, as the work begins with the
central chambers and ends with those on the circumference, the laying
of the females, destined for the large cells, must precede that of
the males, destined for the small cells. So the females come first
and the males at the finish.
This is all very well when the mother herself founds the dwelling,
when she lays the first rows of bricks. But, when she is in the
presence of an old nest, of which she is quite unable to alter the
general arrangement, how is she to make use of the few vacant rooms,
the large and the small alike, if the sex of the egg be already
irrevocably fixed? She can only do so by abandoning the arrangement
in two consecutive rows and accommodating her laying to the varied
exigencies of the home. Either she finds it impossible to make an
economical use of the old nest, a theory refuted by the evidence, or
else she determines at will the sex of the egg which she is about to
lay.
The Osmiae themselves will furnish the most conclusive evidence on
the latter point. We have seen that these Bees are not generally
miners, who themselves dig out the foundation of their cells. They
make use of the old structures of others, or else of natural
retreats, such as hollow stems, the spirals of empty shells and
various hiding-places in walls, clay or wood. Their work is confined
to repairs to the house, such as partitions and covers. There are
plenty of these retreats; and the insect would always find first-
class ones if it thought of going any distance to look for them. But
the Osmia is a stay-at-home: she returns to her birth-place and
clings to it with a patience extremely difficult to exhaust. It is
here, in this little familiar corner, that she prefers to settle her
progeny. But then the apartments are few in number and of all shapes
and sizes. There are long and short ones, spacious ones and narrow.
Short of expatriating herself, a Spartan course, she has to use them
all, from first to last, for she has no choice. Guided by these
considerations, I embarked on the experiments which I will now
describe.
I have said how my study, on two separate occasions, became a
populous hive, in which the Three-horned Osmia built her nests in the
various appliances which I had prepared for her. Among these
appliances, tubes, either of glass or reed, predominated. There were
tubes of all lengths and widths. In the long tubes, entire or almost
entire layings, with a series of females followed by a series of
males, were deposited. As I have already referred to this result, I
will not discuss it again. The short tubes were sufficiently varied
in length to lodge one or other portion of the total laying. Basing
my calculations on the respective lengths of the cocoons of the two
sexes, on the thickness of the partitions and the final lid, I
shortened some of these to the exact dimensions required for two
cocoons only, of different sexes.
Well, these short tubes, whether of glass or reed, were seized upon
as eagerly as the long tubes. Moreover, they yielded this splendid
result: their contents, only a part of the total laying, always began
with female and ended with male cocoons. This order was invariable;
what varied was the number of cells in the long tubes and the
proportion between the two sorts of cocoons, sometimes males
predominating and sometimes females.
The experiment is of paramount importance; and it will perhaps make
the result clearer if I quote one instance from among a multitude of
similar cases. I give the preference to this particular instance
because of the rather exceptional fertility of the laying. An Osmia
marked on the thorax is watched, day by day, from the commencement to
the end of her work. From the 1st to the 10th of May, she occupies a
glass tube in which she lodges seven females followed by a male,
which ends the series. From the 10th to the 17th of May, she
colonizes a second tube, in which she lodges first three females and
then three males. From the 17th to the 25th of May, a third tube,
with three females and then two males. On the 26th of May, a fourth
tube, which she abandons, probably because of its excessive width,
after laying one female in it. Lastly, from the 26th to the 30th of
May, a fifth tube, which she colonizes with two females and three
males. Total: twenty-five Osmiae, including seventeen females and
eight males. And it will not be superfluous to observe that these
unfinished series do not in any way correspond with periods separated
by intervals of rest. The laying is continuous, in so far as the
variable condition of the atmosphere allows. As soon as one tube is
full and closed, another is occupied by the Osmia without delay.
The tubes reduced to the exact length of two cells fulfilled my
expectation in the great majority of cases: the lower cell was
occupied by a female and the upper by a male. There were a few
exceptions. More discerning than I in her estimate of what was
strictly necessary, better-versed in the economy of space, the Osmia
had found a way of lodging two females where I had only seen room for
one female and a male.
This experiment speaks volumes. When confronted with tubes too small
to receive all her family, she is in the same plight as the Mason-bee
in the presence of an old nest. She thereupon acts exactly as the
Chalicodoma does. She breaks up her laying, divides it into series as
short as the room at her disposal demands; and each series begins
with females and ends with males. This breaking up, on the one hand,
into sections in all of which both sexes are represented and the
division, on the other hand, of the entire laying into just two
groups, one female, the other male, when the length of the tube
permits, surely provide us with ample evidence of the insect's power
to regulate the sex of the egg according to the exigencies of space.
And besides the exigencies of space one might perhaps venture to add
those connected with the earlier development of the males. These
burst their cocoons a couple of weeks or more before the females;
they are the first who hasten to the sweets of the almond-tree. In
order to release themselves and emerge into the glad sunlight without
disturbing the string of cocoons wherein their sisters are still
sleeping, they must occupy the upper end of the row; and this, no
doubt, is the reason that makes the Osmia end each of her broken
layings with males. Being next to the door, these impatient ones will
leave the home without upsetting the shells that are slower in
hatching.
I experimented on Latreille's Osmia, using short and even very short
stumps of reed. All that I had to do was to lay them just beside the
nests of the Mason-bee of the Sheds, nests beloved by this particular
Osmia. Old, disused hurdles supplied me with reeds inhabited from end
to end by the Horned Osmia. In both cases I obtained the same results
and the same conclusions as with the Three-horned Osmia.
I return to the latter, nidifying under my eyes in some old nests of
the Mason-bee of the Walls, which I had placed within her reach,
mixed up with the tubes. Outside my study, I had never yet seen the
Three-horned Osmia adopt that domicile. This may be due to the fact
that these nests are isolated one by one in the fields; and the
Osmia, who loves to feel herself surrounded by her kin and to work in
plenty of company, refuses them because of this isolation. But on my
table, finding them close to the tubes in which the others are
working, she adopts them without hesitation.
The chambers presented by those old nests are more or less spacious
according to the thickness of the coat of mortar which the
Chalicodoma has laid over the assembled chambers. To leave her cell,
the Mason-bee has to perforate not only the plug, the lid built at
the mouth of the cell, but also the thick plaster wherewith the dome
is strengthened at the end of the work. The perforation results in a
vestibule which gives access to the chamber itself. It is this
vestibule which is sometimes longer and sometimes shorter, whereas
the corresponding chamber is of almost constant dimensions, in the
case of the same sex, of course.
We will first consider the short vestibule, at the most large enough
to receive the plug with which the Osmia will close up the lodging.
There is then nothing at her disposal except the cell proper, a
spacious apartment in which one of the Osmia's females will find
ample accommodation, for she is much smaller than the original
occupant of the chamber, no matter the sex; but there is not room for
two cocoons at a time, especially in view of the space taken up by
the intervening partition. Well, in those large, well-built chambers,
formerly the homes of Chalicodomae, the Osmia settles females and
none but females.
Let us now consider the long vestibule. Here, a partition is
constructed, encroaching slightly on the cell proper, and the
residence is divided into two unequal storeys, a large room below,
housing a female, and a narrow cabin above, containing a male.
When the length of the vestibule permits, allowing for the space
required by the outer stopper, a third storey is built, smaller than
the second; and another male is lodged in this cramped corner. In
this way the old nest of the Mason-bee of the Pebbles is colonized,
cell after cell, by a single mother.
The Osmia, as we see, is very frugal of the lodging that has fallen
to her share; she makes the best possible use of it, giving to the
females the spacious chambers of the Mason-bee and to the males the
narrow vestibules, subdivided into storeys when this is feasible.
Economy of space is the chief consideration, since her stay-at-home
tastes do not allow her to indulge in distant quests. She has to
employ the site which chance places at her disposal just as it is,
now for a male and now for a female. Here we see displayed, more
clearly than ever, her power of deciding the sex of the egg, in order
to adapt it judiciously to the conditions of the house-room
available.
I had offered at the same time to the Osmiae in my study some old
nests of the Mason-bee of the Shrubs, which are clay spheroids with
cylindrical cavities in them. These cavities are formed, as in the
old nests of the Mason-bee of the Pebbles, of the cell properly so-
called and of the exit-way which the perfect insect cut through the
outer coating at the time of its deliverance. Their diameter is about
seven millimetres (.273 inch.--Translator's Note.); their depth at
the centre of the heap is 23 millimetres (.897 inch.--Translator's
Note.); and at the edge averages 14 millimetres (.546 inch.--
Translator's Note.)
The deep central cells receive only the females of the Osmia;
sometimes even the two sexes together, with a partition in the
middle, the female occupying the lower and the male the upper storey.
True, in such cases economy of space is strained to the utmost, the
apartments provided by the Mason-bee of the Shrubs being very small
as it is, despite their entrance-halls. Lastly, the deeper cavities
on the circumference are allotted to females and the shallower to
males.
I will add that a single mother peoples each nest and also that she
proceeds from cell to cell without troubling to ascertain the depth.
She goes from the centre to the edges, from the edges to the centre,
from a deep cavity to a shallow cavity and vice versa, which she
would not do if the sexes were to follow upon each other in a settled
order. For greater certainty, I numbered the cells of one nest as
each of them was closed. On opening them later, I was able to see
that the sexes were not subjected to a chronological arrangement.
Females were succeeded by males and these by females without its
being possible for me to make out any regular sequence. Only--and
this is the essential point--the deep cavities were allotted to the
females and the shallow ones to the males.
We know that the Three-horned Osmia prefers to haunt the habitations
of the Bees who nidify in populous colonies, such as the Mason-bee of
the Sheds and the Hairy-footed Anthophora. Exercising the very
greatest care, I broke up some great lumps of earth removed from the
banks inhabited by the Anthophora and sent to me from Carpentras by
my dear friend and pupil M. Devillario. I examined them
conscientiously in the quiet of my study. I found the Osmia's cocoons
arranged in short series, in very irregular passages, the original
work of which is due to the Anthophora. Touched up afterwards, made
larger or smaller, lengthened or shortened, intersected with a
network of crossings by the numerous generations that had succeeded
one another in the same city, they formed an inextricable labyrinth.
Sometimes these corridors did not communicate with any adjoining
apartment; sometimes they gave access to the spacious chamber of the
Anthophora, which could be recognized, in spite of its age, by its
oval shape and its coating of glazed stucco. In the latter case, the
bottom cell, which once constituted, by itself, the chamber of the
Anthophora, was always occupied by a female Osmia. Beyond it, in the
narrow corridor, a male was lodged, not seldom two, or even three. Of
course, clay partitions, the work of the Osmia, separated the
different inhabitants, each of whom had his own storey, his own
closed cell.
When the accommodation consisted of no more than a simple cylinder,
with no state-bedroom at the end of it--a bedroom always reserved for
a female--the contents varied with the diameter of the cylinder. The
series, of which the longest were series of four, included, with a
wider diameter, first one or two females, then one or two males. It
also happened, though rarely, that the series was reversed, that is
to say, it began with males and ended with females. Lastly, there
were a good many isolated cocoons, of one sex or the other. When the
cocoon was alone and occupied the Anthophora's cell, it invariably
belonged to a female.
I have observed the same thing in the nests of the Mason-bee of the
Sheds, but not so easily. The series are shorter here, because the
Mason-bee does not bore galleries but builds cell upon cell. The work
of the whole swarm thus forms a stratum of cells that grows thicker
from year to year. The corridors occupied by the Osmia are the holes
which the Mason-bee dug in order to reach daylight from the deep
layers. In these short series, both sexes are usually present; and,
if the Mason-bee's chamber is at the end of the passage, it is
inhabited by a female Osmia.
We come back to what the short tubes and the old nests of the Mason-
bee of the Pebbles have already taught us. The Osmia who, in tubes of
sufficient length, divides her whole laying into a continuous
sequence of females and a continuous sequence of males, now breaks it
up into short series in which both sexes are present. She adapts her
sectional layings to the exigencies of a chance lodging; she always
places a female in the sumptuous chamber which the Mason-bee or the
Anthophora occupied originally.
Facts even more striking are supplied by the old nests of the Masked
Anthophora (A. personata, ILLIG.), old nests which I have seen
utilized by the Horned Osmia and the Three-horned Osmia at the same
time. Less frequently, the same nests serve for Latreille's Osmia.
Let us first describe the Masked Anthophora's nests.
In a steep bank of sandy clay, we find a set of round, wide-open
holes. There are generally only a few of them, each about half an
inch in diameter. They are the entrance-doors leading to the
Anthophora's abode, doors always left open, even after the building
is finished. Each of them gives access to a short passage, sometimes
straight, sometimes winding, nearly horizontal, polished with minute
care and varnished with a sort of white glaze. It looks as if it had
received a thin coat of whitewash. On the inner surface of this
passage, in the thickness of the earthy bank, spacious oval niches
have been excavated, communicating with the corridor by means of a
narrow bottle-neck, which is closed, when the work is done, with a
substantial mortar stopper. The Anthophora polishes the outside of
this stopper so well, smooths its surface so perfectly, bringing it
to the same level as that of the passage, is so careful to give it
the white tint of the rest of the wall that, when the job is
finished, it becomes absolutely impossible to distinguish the
entrance-door corresponding with each cell.
The cell is an oval cavity dug in the earthy mass. The wall has the
same polish, the same chalky whiteness as the general passage. But
the Anthophora does not limit herself to digging oval niches: to make
her work more solid, she pours over the walls of the chamber a
salivary liquid which not only whitens and varnishes but also
penetrates to a depth of some millimetres into the sandy earth, which
it turns into a hard cement. A similar precaution is taken with the
passage; and therefore the whole is a solid piece of work capable of
remaining in excellent condition for years.
Moreover, thanks to the wall hardened by the salivary fluid, the
structure can be removed from its matrix by chipping it carefully
away. We thus obtain, at least in fragments, a serpentine tube from
which hangs a single or double row of oval nodules that look like
large grapes drawn out lengthwise. Each of these nodules is a cell,
the entrance to which, carefully hidden, opens into the tube or
passage. When she wishes to leave her cell, in the spring, the
Anthophora destroys the mortar disk that closes the jar and thus
reaches the general corridor, which is quite open to the outer air.
The abandoned nest provides a series of pear-shaped cavities, of
which the distended part is the old cell and the contracted part the
exit-neck, rid of its stopper.
These pear-shaped hollows form splendid lodgings, impregnable
strongholds, in which the Osmiae find a safe and commodious retreat
for their families. The Horned Osmia and the Three-horned Osmia
establish themselves there at the same time. Although it is a little
too large for her, Latrielle's Osmia also appears very well satisfied
with it.
I have examined some forty of the superb cells utilized by each of
the first two. The great majority are divided into two storeys by
means of a transversal partition. The lower storey includes the
larger portion of the Anthophora's cell; the upper storey includes
the rest of the cell and a little of the bottle-neck that surmounts
it. The two-roomed dwelling is closed, in the passage, by a
shapeless, bulky mass of dried mud. What a clumsy artist the Osmia
is, compared with the Anthophora! Against the exquisite work of the
Anthophora, partition and plug strike a note as hideously incongruous
as a lump of dirt on polished marble.
The two apartments thus obtained are of a very unequal capacity,
which at once strikes the observer. I measured them with my five-
millimetre tube. On an average, the bottom one is represented by a
column of sand 50 millimetres deep (1.95 inches.--Translator's Note.)
and the top one by a column of 15 millimetres (.585 inch.--
Translator's Note.). The holding-capacity of the one is therefore
about three times as large as that of the other. The cocoons enclosed
present the same disparity. The bottom one is big, the top one small.
Lastly, the lower one belongs to a female Osmia and the upper to a
male Osmia.
Occasionally the length of the bottle-neck allows of a fresh
arrangement and the cavity is divided into three storeys. The bottom
one, which is always the most spacious, contains a female; the two
above, both smaller than the first and one smaller than the other,
contain males.
Let us keep to the first case, which is always the most frequent. The
Osmia is in the presence of one of these pear-shaped hollows. It is a
find that must be employed to the best advantage: a prize of this
sort is rare and falls only to fortune's favourites. To lodge two
females in it at once is impossible; there is not sufficient room. To
lodge two males in it would be undue generosity to a sex that is
entitled to but the smallest consideration. Besides, the two sexes
must be represented in almost equal numbers. The Osmia decides upon
one female, whose portion shall be the better room, the lower one,
which is larger, better-protected and more nicely polished, and one
male, whose portion shall be the upper storey, a cramped attic,
uneven and rugged in the part which encroaches on the bottle-neck.
This decision is proved by numerous undeniable facts. Both Osmiae
therefore can choose the sex of the egg about to be laid, seeing that
they are now breaking up the laying into groups of two, a female and
a male, as required by the conditions of the lodging.
I have only once found Latreille's Osmia established in the nest of
the Masked Anthophora. She had occupied but a small number of cells,
because the others were not free, being inhabited by the Anthophora.
The cells in question were divided into three storeys by partitions
of green mortar; the lower storey was occupied by a female, the two
others by males, with smaller cocoons.
I came to an even more remarkable example. Two Anthidia of my
district, A. septemdentatum, LATR., and A. bellicosum, LEP., adopt as
the home of their offspring the empty shells of different snails:
Helix aspersa, H. algira, H. nemoralis, H. caespitum. The first-
named, the Common Snail, is the most often used, under the stone-
heaps and in the crevices of old walls. Both Anthidia colonize only
the second whorl of the spiral. The central part is too small and
remains unoccupied. Even so with the front whorl, the largest, which
is left completely empty, so much so that, on looking through the
opening, it is impossible to tell whether the shell does or does not
contain the Bee's nest. We have to break this last whorl if we would
perceive the curious nest tucked away in the spiral.
We then find first a transversal partition, formed of tiny bits of
gravel cemented by a putty made from resin, which is collected in
fresh drops from the oxycedrus and the Aleppo pine. Beyond this is a
stout barricade made up of rubbish of all kinds: bits of gravel,
scraps of earth, juniper-needles, the catkins of the conifers, small
shells, dried excretions of Snails. Next come a partition of pure
resin, a large cocoon in a roomy chamber, a second partition of pure
resin and, lastly, a smaller cocoon in a narrow chamber. The
inequality of the two cells is the necessary consequence of the shape
of the shell, whose inner space gains rapidly in width as the spiral
gets nearer to the orifice. Thus, by the mere general arrangement of
the home and without any work on the Bee's part beyond some slender
partitions, a large room is marked out in front and a much smaller
room at the back.
By a very remarkable exception, which I have mentioned casually
elsewhere, the males of the genus Anthidium are generally larger than
the females; and this is the case with the two species in particular
that divide the Snail's spiral with resin partitions. I collected
some dozens of nests of both species. In at least half the cases, the
two sexes were present together; the female, the smaller, occupied
the front cell and the male, the bigger, the back cell. Other cells,
which were smaller or too much obstructed at the back by the dried-up
remains of the Mollusc, contained only one cell, occupied at one time
by a female and at another by a male. A few, lastly, had both cells
inhabited now by two males and now by two females. The most frequent
arrangement was the simultaneous presence of both sexes, with the
female in front and the male behind. The Anthidia who make resin-
dough and live in Snail-shells can therefore alternate the sexes
regularly to meet the exigencies of the spiral dwelling-house.
One more thing and I have done. My apparatus of reeds, fixed against
the walls of the garden, supplied me with a remarkable nest of the
Horned Osmia. The nest is established in a bit of reed 11 millimetres
wide inside. (.429 inch--Translator's Note.) It comprises thirteen
cells and occupies only half the cylinder, although the orifice is
plugged with the usual stopper. The laying therefore seems here to be
complete.
Well, this laying is arranged in a most singular fashion. There is
first, at a suitable distance from the bottom or the node of the
reed, a transversal partition, perpendicular to the axis of the tube.
This marks off a cell of unusual size, in which a female is lodged.
After that, in view of the excessive width of the tunnel, which is
too great for a series in single file, the Osmia appears to alter her
mind. She therefore builds a partition perpendicular to the
transversal partition which she has just constructed and thus divides
the second storey into two rooms, a larger room, in which she lodges
a female, and a smaller, in which she lodges a male. She next builds
a second transversal partition and a second longitudinal partition
perpendicular to it. These once more give two unequal chambers,
stocked likewise, the large one with a female, the smaller one with a
male.
>From this third storey onwards, the Osmia abandons geometrical
accuracy; the architect seems to be a little out in her reckoning.
The transversal partitions become more and more slanting and the work
grows irregular, but always with a sprinkling of large chambers for
the females and small chambers for the males. Three females and two
males are housed in this way, the sexes alternating.
By the time that the base of the eleventh cell is reached, the
transversal partition is once more almost perpendicular to the axis.
Here what happened at the bottom is repeated. There is no
longitudinal partition; and the spacious cell, covering the whole
diameter of the cylinder, receives a female. The edifice ends with
two transversal partitions and one longitudinal partition, which mark
out, on the same level, chambers twelve and thirteen, both of which
contain males.
There is nothing more curious than this mixing of the two sexes, when
we know with what precision the Osmia separates them in a linear
series, where the narrow width of the cylinder demands that the cells
shall be set singly, one above the other. Here, the Bee is making use
of a tube whose diameter is not suited to her work; she is
constructing a complex and difficult edifice, which perhaps would not
possess the necessary solidity if the ceilings were too broad. The
Osmia therefore supports these ceilings with longitudinal partitions;
and the unequal chambers resulting from the introduction of these
partitions receive females at one time and males at another,
according to their capacity.
CHAPTER 5. PERMUTATIONS OF SEX.
The sex of the egg is optional. The choice rests with the mother, who
is guided by considerations of space and, according to the
accommodation at her disposal, which is frequently fortuitous and
incapable of modification, places a female in this cell and a male in
that, so that both may have a dwelling of a size suited to their
unequal development. This is the unimpeachable evidence of the
numerous and varied facts which I have set forth. People unfamiliar
with insect anatomy--the public for whom I write--would probably give
the following explanation of this marvellous prerogative of the Bee:
the mother has at her disposal a certain number of eggs, some of
which are irrevocably female and the others irrevocably male: she is
able to pick out of either group the one which she wants at the
actual moment; and her choice is decided by the holding capacity of
the cell that has to be stocked. Everything would then be limited to
a judicious selection from the heap of eggs.
Should this idea occur to him, the reader must hasten to reject it.
Nothing could be more false, as the merest reference to anatomy will
show. The female reproductive apparatus of the Hymenoptera consists
generally of six ovarian tubes, something like glove-fingers, divided
into bunches of three and ending in a common canal, the oviduct,
which carries the eggs outside. Each of these glove-fingers is fairly
wide at the base, but tapers sharply towards the tip, which is
closed. It contains, arranged in a row, one after the other, like
beads on a string, a certain number of eggs, five or six for
instance, of which the lower ones are more or less developed, the
middle ones half-way towards maturity, and the upper ones very
rudimentary. Every stage of evolution is here represented,
distributed regularly from bottom to top, from the verge of maturity
to the vague outlines of the embryo. The sheath clasps its string of
ovules so closely that any inversion of the order is impossible.
Besides, an inversion would result in a gross absurdity: the
replacing of a riper egg by another in an earlier stage of
development.
Therefore, in each ovarian tube, in each glove-finger, the emergence
of the eggs occurs according to the order governing their arrangement
in the common sheath; and any other sequence is absolutely
impossible. Moreover, at the nesting period, the six ovarian sheaths,
one by one and each in its turn, have at their base an egg which in a
very short time swells enormously. Some hours or even a day before
the laying, that egg by itself represents or even exceeds in bulk the
whole of the ovigenous apparatus. This is the egg which is on the
point of being laid. It is about to descend into the oviduct, in its
proper order, at its proper time; and the mother has no power to make
another take its place. It is this egg, necessarily this egg and no
other, that will presently be laid upon the provisions, whether these
be a mess of honey or a live prey; it alone is ripe, it alone is at
the entrance to the oviduct; none of the others, since they are
farther back in the row and not at the right stage of development,
can be substituted at this crisis. Its birth is inevitable.
What will it yield, a male or a female? No lodging has been prepared,
no food collected for it; and yet both food and lodging have to be in
keeping with the sex that will proceed from it. And here is a much
more puzzling condition: the sex of that egg, whose advent is
predestined, has to correspond with the space which the mother
happens to have found for a cell. There is therefore no room for
hesitation, strange though the statement may appear: the egg, as it
descends from its ovarian tube, has no determined sex. It is perhaps
during the few hours of its rapid development at the base of its
ovarian sheath, it is perhaps on its passage through the oviduct that
it receives, at the mother's pleasure, the final impress that will
produce, to match the cradle which it has to fill, either a female or
a male.
Thereupon the following question presents itself. Let us admit that,
when the normal conditions remain, a laying would have yielded m
females and n males. Then, if my conclusions are correct, it must be
in the mother's power, when the conditions are different, to take
from the m group and increase the n group to the same extent; it must
be possible for her laying to be represented as m-1, m-2, m-3, etc.
females and by n+1, n+2, n+3, etc. males, the sum of m+n remaining
constant, but one of the sexes being partly permuted into the other.
The ultimate conclusion even cannot be disregarded: we must admit a
set of eggs represented by m-m, or zero, females and of n+m males,
one of the sexes being completely replaced by the other. Conversely,
it must be possible for the feminine series to be augmented from the
masculine series to the extent of absorbing it entirely. It was to
solve this question and some others connected with it that I
undertook, for the second time, to rear the Three-horned Osmia in my
study.
The problem on this occasion is a more delicate one; but I am also
better-equipped. My apparatus consists of two small, closed packing-
cases, with the front side of each pierced with forty holes, in which
I can insert my glass tubes and keep them in a horizontal position. I
thus obtain for the Bees the darkness and mystery which suit their
work and for myself the power of withdrawing from my hive, at any
time, any tube that I wish, with the Osmia inside, so as to carry it
to the light and follow, if need be with the aid of the lens, the
operations of the busy worker. My investigations, however frequent
and minute, in no way hinder the peaceable Bee, who remains absorbed
in her maternal duties.
I mark a plentiful number of my guests with a variety of dots on the
thorax, which enables me to follow any one Osmia from the beginning
to the end of her laying. The tubes and their respective holes are
numbered; a list, always lying open on my desk, enables me to note
from day to day, sometimes from hour to hour, what happens in each
tube and particularly the actions of the Osmiae whose backs bear
distinguishing marks. As soon as one tube is filled, I replace it by
another. Moreover, I have scattered in front of either hive a few
handfuls of empty Snail-shells, specially chosen for the object which
I have in view. Reasons which I will explain later led me to prefer
the shells of Helix caespitum. Each of the shells, as and when
stocked, received the date of the laying and the alphabetical sign
corresponding with the Osmia to whom it belonged. In this way, I
spent five or six weeks in continual observation. To succeed in an
enquiry, the first and foremost condition is patience. This condition
I fulfilled; and it was rewarded with the success which I was
justified in expecting.
The tubes employed are of two kinds. The first, which are cylindrical
and of the same width throughout, will be of use for confirming the
facts observed in the first year of my experiments in indoor rearing.
The others, the majority, consist of two cylinders which are of very
different diameters, set end to end. The front cylinder, the one
which projects a little way outside the hive and forms the entrance-
hole, varies in width between 8 and 12 millimetres. (Between .312 to
.468 inch.--Translator's Note.) The second, the back one, contained
entirely within my packing-case, is closed at its far end and is 5 to
6 millimetres (.195 to .234 inch.--Translator's Note.) in diameter.
Each of the two parts of the double-galleried tunnel, one narrow and
one wide, measures at most a decimetre (3.9 inches.--Translator's
Note.) in length. I thought it advisable to have these short tubes,
as the Osmia is thus compelled to select different lodgings, each of
them being insufficient in itself to accommodate the total laying. In
this way I shall obtain a greater variety in the distribution of the
sexes. Lastly, at the mouth of each tube, which projects slightly
outside the case, there is a little paper tongue, forming a sort of
perch on which the Osmia alights on her arrival and giving easy
access to the house. With these facilities, the swarm colonized
fifty-two double-galleried tubes, thirty-seven cylindrical tubes,
seventy-eight Snail-shells and a few old nests of the Mason-bee of
the Shrubs. From this rich mine of material I will take what I want
to prove my case.
Every series, even when incomplete, begins with females and ends with
males. To this rule I have not yet found an exception, at least in
galleries of normal diameter. In each new abode, the mother busies
herself first of all with the more important sex. Bearing this point
in mind, would it be possible for me, by manoeuvring, to obtain an
inversion of this order and make the laying begin with males? I think
so, from the results already ascertained and the irresistible
conclusions to be drawn from them. The double-galleried tubes are
installed in order to put my conjectures to the proof.
The back gallery, 5 or 6 millimetres (.195 to .234 inch.--
Translator's Note.) wide, is too narrow to serve as a lodging for
normally developed females. If, therefore, the Osmia, who is very
economical of her space, wishes to occupy them, she will be obliged
to establish males there. And her laying must necessarily begin here,
because this corner is the rear-most part of the tube. The foremost
gallery is wide, with an entrance-door on the front of the hive.
Here, finding the conditions to which she is accustomed, the mother
will go on with her laying in the order which she prefers.
Let us now see what has happened. Of the fifty-two double galleried
tubes, about a third did not have their narrow passage colonized. The
Osmia closed its aperture communicating with the large passage; and
the latter alone received the eggs. This waste of space was
inevitable. The female Osmiae, though nearly always larger than the
males, present marked differences among one another: some are bigger,
some are smaller. I had to adjust the width of the narrow galleries
to Bees of average dimensions. It may happen therefore that a gallery
is too small to admit the large-sized mothers to whom chance allots
it. When the Osmia is unable to enter the tube, obviously she will
not colonize it. She then closes the entrance to this space which she
cannot use and does her laying beyond it, in the wide tube. Had I
tried to avoid these useless apparatus by choosing tubes of larger
calibre, I should have encountered another drawback: the medium-sized
mothers, finding themselves almost comfortable, would have decided to
lodge females there. I had to be prepared for it: as each mother
selected her house at will and as I was unable to interfere in her
choice, a narrow tube would be colonized or not, according as the
Osmia who owned it was or was not able to make her way inside.
There remain some forty pairs of tubes with both galleries colonized.
In these there are two things to take into consideration. The narrow
rear tubes of 5 or 5 1/2 millimetres (.195 to .214 inch.--
Translator's Note.)--and these are the most numerous--contain males
and males only, but in short series, between one and five. The mother
is here so much hampered in her work that they are rarely occupied
from end to end; the Osmia seems in a hurry to leave them and to go
and colonize the front tube, whose ample space will leave her the
liberty of movement necessary for her operations. The other rear
tubes, the minority, whose diameter is about 6 millimetres (.234
inch.--Translator's Note.), contain sometimes only females and
sometimes females at the back and males towards the opening. One can
see that a tube a trifle wider and a mother slightly smaller would
account for this difference in the results. Nevertheless, as the
necessary space for a female is barely provided in this case, we see
that the mother avoids as far as she can a two-sex arrangement
beginning with males and that she adopts it only in the last
extremity. Finally, whatever the contents of the small tube may be,
those of the large one, following upon it, never vary and consist of
females at the back and males in front.
Though incomplete, because of circumstances very difficult to
control, the result of the experiment is none the less very striking.
Twenty-five apparatus contain only males in their narrow gallery, in
numbers varying from a minimum of one to a maximum of five. After
these comes the colony of the large gallery, beginning with females
and ending with males. And the layings in these apparatus do not
always belong to late summer or even to the intermediate period: a
few small tubes contain the earliest eggs of the Osmiae. A couple of
Osmiae, more forward than the others, set to work on the 23rd of
April. Both of them started their laying by placing males in the
narrow tubes. The meagre supply of provisions was enough in itself to
show the sex, which proved later to be in accordance with my
anticipations. We see then that, by my artifices, the whole swarm
starts with the converse of the normal order. This inversion is
continued, at no matter what period, from the beginning to the end of
the operations. The series which, according to rule, would begin with
females now begins with males. Once the larger gallery is reached,
the laying is pursued in the usual order.
We have advanced one step and that no small one: we have seen that
the Osmia, when circumstances require it, is capable of reversing the
sequence of the sexes. Would it be possible, provided that the tube
were long enough, to obtain a complete inversion, in which the entire
series of the males should occupy the narrow gallery at the back and
the entire series of the females the roomy gallery in front? I think
not; and I will tell you why.
Long and narrow cylinders are by no means to the Osmia's taste, not
because of their narrowness but because of their length. Remember
that for each load of honey brought the worker is obliged to move
backwards twice. She enters, head first, to begin by disgorging the
honey-syrup from her crop. Unable to turn in a passage which she
blocks entirely, she goes out backwards, crawling rather than
walking, a laborious performance on the polished surface of the glass
and a performance which, with any other surface, would still be very
awkward, as the wings are bound to rub against the wall with their
free end and are liable to get rumpled or bent. She goes out
backwards, reaches the outside, turns round and goes in again, but
this time the opposite way, so as to brush off the load of pollen
from her abdomen on to the heap. If the gallery is at all long, this
crawling backwards becomes troublesome after a time; and the Osmia
soon abandons a passage that is too small to allow of free movement.
I have said that the narrow tubes of my apparatus are, for the most
part, only very incompletely colonized. The Bee, after lodging a
small number of males in them, hastens to leave them. In the wide
front gallery, she can stay where she is and still be able to turn
round easily for her different manipulations; she will avoid those
two long journeys backwards, which are so exhausting and so bad for
her wings.
Another reason no doubt prompts her not to make too great a use of
the narrow passage, in which she would establish males, followed by
females in the part where the gallery widens. The males have to leave
their cells a couple of weeks or more before the females. If they
occupy the back of the house, they will die prisoners or else they
will overturn everything on their way out. This risk is avoided by
the order which the Osmia adopts.
In my tubes with their unusual arrangement, the mother might well
find the dilemma perplexing: there is the narrowness of the space at
her disposal and there is the emergence later on. In the narrow
tubes, the width is insufficient for the females; on the other hand,
if she lodges males there, they are liable to perish, since they will
be prevented from issuing at the proper moment. This would perhaps
explain the mother's hesitation and her obstinacy in settling females
in some of my apparatus which looked as if they could suit none but
males.
A suspicion occurs to me, a suspicion aroused by my attentive
examination of the narrow tubes. All, whatever the number of their
inmates, are carefully plugged at the opening, just as separate tubes
would be. It might therefore be the case that the narrow gallery at
the back was looked upon by the Osmia not as the prolongation of the
large front gallery, but as an independent tube. The facility with
which the worker turns as soon as she reaches the wide tube, her
liberty of action, which is now as great as in a doorway
communicating with the outer air, might well be misleading and cause
the Osmia to treat the narrow passage at the back as though the wide
passage in front did not exist. This would account for the placing of
the female in the large tube above the males in the small tube, an
arrangement contrary to her custom.
I will not undertake to decide whether the mother really appreciates
the danger of my snares, or whether she makes a mistake in
considering only the space at her disposal and beginning with males.
At any rate, I perceive in her a tendency to deviate as little as
possible from the order which safeguards the emergence of the two
sexes. This tendency is demonstrated by her repugnance to colonizing
my narrow tubes with long series of males. However, so far as we are
concerned, it does not matter much what passes at such times in the
Osmia's little brain. Enough for us to know that she dislikes narrow
and long tubes, not because they are narrow, but because they are at
the same time long.
And, in fact, she does very well with a short tube of the same
diameter. Such are the cells in the old nests of the Mason-bee of the
Shrubs and the empty shells of the Garden Snail. With the short tube,
the two disadvantages of the long tube are avoided. She has very
little of that crawling backwards to do when she has a Snail-shell
for the home of her eggs and scarcely any when the home is the cell
of the Mason-bee. Moreover, as the stack of cocoons numbers two or
three at most, the deliverance will be exempt from the difficulties
attached to a long series. To persuade the Osmia to nidify in a
single tube long enough to receive the whole of her laying and at the
same time narrow enough to leave her only just the possibility of
admittance appears to me a project without the slightest chance of
success: the Bee would stubbornly refuse such a dwelling or would
content herself with entrusting only a very small portion of her eggs
to it. On the other hand, with narrow but short cavities, success,
without being easy, seems to me at least quite possible. Guided by
these considerations, I embarked upon the most arduous part of my
problem: to obtain the complete or almost complete permutation of one
sex with the other; to produce a laying consisting only of males by
offering the mother a series of lodgings suited only to males.
Let us in the first place consult the old nests of the Mason-bee of
the Shrubs. I have said that these mortar spheroids, pierced all over
with little cylindrical cavities, are adopted pretty eagerly by the
Three-horned Osmia, who colonizes them before my eyes with females in
the deep cells and males in the shallow cells. That is how things go
when the old nest remains in its natural state. With a grater,
however, I scrape the outside of another nest so as to reduce the
depth of the cavities to some ten millimetres. (About two-fifths of
an inch.--Translator's Note.) This leaves in each cell just room for
one cocoon, surmounted by the closing stopper. Of the fourteen
cavities in the nests, I leave two intact, measuring fifteen
millimetres in depth. (.585 inch.--Translator's Note.) Nothing could
be more striking than the result of this experiment, made in the
first year of my home rearing. The twelve cavities whose depth had
been reduced all received males; the two cavities left untouched
received females.
A year passes and I repeat the experiment with a nest of fifteen
cells; but this time all the cells are reduced to the minimum depth
with the grater. Well, the fifteen cells, from first to last, are
occupied by males. It must be quite understood that, in each case,
all the offspring belonged to one mother, marked with her
distinguishing spot and kept in sight as long as her laying lasted.
He would indeed be difficult to please who refused to bow before the
results of these two experiments. If, however, he is not yet
convinced, here is something to remove his last doubts.
The Three-horned Osmia often settles her family in old shells,
especially those of the Common Snail (Helix aspersa), who is so
common under the stone-heaps and in the crevices of the little
unmortared walls that support our terraces. In this species, the
spiral is wide open, so that the Osmia, penetrating as far down as
the helical passage permits, finds, immediately above the point which
is too narrow to pass, the space necessary for the cell of a female.
This cell is succeeded by others, wider still, always for females,
arranged in a line in the same way as in a straight tube. In the last
whorl of the spiral, the diameter would be too great for a single
row. Then longitudinal partitions are added to the transverse
partitions, the whole resulting in cells of unequal dimensions in
which males predominate, mixed with a few females in the lower
storeys. The sequence of the sexes is therefore what it would be in a
straight tube and especially in a tube with a wide bore, where the
partitioning is complicated by subdivisions on the same level. A
single Snail-shell contains room for six or eight cells. A large,
rough earthen stopper finishes the nest at the entrance to the shell.
As a dwelling of this sort could show us nothing new, I chose for my
swarm the Garden Snail (Helix caespitum), whose shell, shaped like a
small, swollen Ammonite, widens by slow degrees, the diameter of the
usable portion, right up to the mouth, being hardly greater than that
required by a male Osmia-cocoon. Moreover, the widest part, in which
a female might find room, has to receive a thick stopping-plug, below
which there will often be a free space. Under all these conditions,
the house will hardly suit any but males arranged one after the
other.
The collection of shells placed at the foot of each hive includes
specimens of different sizes. The smallest are 18 millimetres (.7
inch.--Translator's Note.) in diameter and the largest 24 millimetres
(.936 inch.--Translator's Note.) There is room for two cocoons, or
three at most, according to their dimensions.
Now these shells were used by my visitors without any hesitation,
perhaps even with more eagerness than the glass tubes, whose slippery
sides might easily be a little annoying to the Bee. Some of them were
occupied on the first few days of the laying; and the Osmia who had
started with a home of this sort would pass next to a second Snail-
shell, in the immediate neighbourhood of the first, to a third, a
fourth and others still, always close to one another, until her
ovaries were emptied. The whole family of one mother would thus be
lodged in Snail-shells which were duly marked with the date of the
laying and a description of the worker. The faithful adherents of the
Snail-shell were in the minority. The greater number left the tubes
to come to the shells and then went back from the shells to the
tubes. All, after filling the spiral staircase with two or three
cells, closed the house with a thick earthen stopper on a level with
the opening. It was a long and troublesome task, in which the Osmia
displayed all her patience as a mother and all her talents as a
plasterer. There were even some who, scrupulous to excess, carefully
cemented the umbilicus, a hole which seemed to inspire them with
distrust as being able to give access to the interior of the
dwelling. It was a dangerous-looking cavity, which for the greater
safety of the family it was prudent to block up.
When the pupae are sufficiently matured, I proceed to examine these
elegant abodes. The contents fill me with joy: they fulfil my
anticipations to the letter. The great, the very great majority of
the cocoons turn out to be males; here and there, in the bigger
cells, a few rare females appear. The smallness of the space has
almost done away with the sixty-eight Snail-shells colonized. But, of
this total number, I must use only those series which received an
entire laying and were occupied by the same Osmia from the beginning
to the end of the egg-season. Here are a few examples, taken from
among the most conclusive.
>From the 6th of May, when she started operations, to the 25th of May,
the date at which her laying ceased, the Osmia occupied seven Snail-
shells in succession. Her family consists of fourteen cocoons, a
number very near the average; and, of these fourteen cocoons, twelve
belong to males and only two to females. These occupy the seventh and
thirteenth places in chronological order.
Another, between the 9th and 27th of May, stocked six Snail-shells
with a family of thirteen, including ten males and three females. The
places occupied by the latter in the series were numbers 3, 4 and 5.
A third, between the 2nd and 29th of May, colonized eleven Snail-
shells, a prodigious task. This industrious one was also exceedingly
prolific. She supplied me with a family of twenty-six, the largest
which I have ever obtained from one Osmia. Well, this abnormal
progeny consisted of twenty-five males and one female, one alone,
occupying place 17.
There is no need to go on, after this magnificent example, especially
as the other series would all, without exception, give us the same
result. Two facts are immediately obvious. The Osmia is able to
reverse the order of her laying and to start with a more or less long
series of males before producing any females. In the first case, the
first female appears as number 7; in the third, as number 17. There
is something better still; and this is the proposition which I was
particularly anxious to prove: the female sex can be permuted with
the male sex and can be permuted to the point of disappearing
altogether. We see this especially in the third case, where the
presence of a solitary female in a family of twenty-six is due to the
somewhat larger diameter of the corresponding Snail-shell and also,
no doubt, to some mistake on the mother's part, for the female
cocoon, in a series of two, occupies the upper storey, the one next
to the orifice, an arrangement which the Osmia appears to me to
dislike.
This result throws so much light on one of the darkest corners of
biology that I must attempt to corroborate it by means of even more
conclusive experiments. I propose next year to give the Osmiae
nothing but Snail-shells for a lodging, picked out one by one, and
rigorously to deprive the swarm of any other retreat in which the
laying could be effected. Under these conditions, I ought to obtain
nothing but males, or nearly, for the whole swarm.
There would still remain the inverse permutation: to obtain only
females and no males, or very few. The first permutation makes the
second seem very probable, although I cannot as yet conceive a means
of realizing it. The only condition which I can regulate is the
dimensions of the home. When the rooms are small, the males abound
and the females tend to disappear. With generous quarters, the
converse would not take place. I should obtain females and afterwards
an equal number of males, confined in small cells which, in case of
need, would be bounded by numerous partitions. The factor of space
does not enter into the question here. What artifice can we then
employ to provoke this second permutation? So far, I can think of
nothing that is worth attempting.
It is time to conclude. Leading a retired life, in the solitude of a
village, having quite enough to do with patiently and obscurely
ploughing my humble furrow, I know little about modern scientific
views. In my young days I had a passionate longing for books and
found it difficult to procure them; to-day, when I could almost have
them if I wanted, I am ceasing to wish for them. It is what usually
happens as life goes on. I do not therefore know what may have been
done in the direction whither this study of the sexes has led us. If
I am stating propositions that are really new or at least more
comprehensive than the propositions already known, my words will
perhaps sound heretical. No matter: as a simple translator of facts,
I do not hesitate to make my statement, being fully persuaded that
time will turn my heresy into orthodoxy. I will therefore
recapitulate my conclusions.
Bees lay their eggs in series of first females and then males, when
the two sexes are of different sizes and demand an unequal quantity
of nourishment. When the two sexes are alike in size, the same
sequence may occur, but less regularly.
This dual arrangement disappears when the place chosen for the nest
is not large enough to contain the entire laying. We then see broken
layings, beginning with females and ending with males.
The egg, as it issues from the ovary, has not yet a fixed sex. The
final impress that produces the sex is given at the moment of laying
or a little before.
So as to be able to give each larva the amount of space and food that
suits it according as it is male or female, the mother can choose the
sex of the egg which she is about to lay. To meet the conditions of
the building, which is often the work of another or else a natural
retreat that admits of little or no alteration, she lays either a
male egg or a female egg as she pleases. The distribution of the
sexes depends upon herself. Should circumstances require it, the
order of the laying can be reversed and begin with males; lastly, the
entire laying can contain only one sex.
The same privilege is possessed by the predatory Hymenoptera, the
Wasps, at least by those in whom the two sexes are of a different
size and consequently require an amount of nourishment that is larger
in the one case than in the other. The mother must know the sex of
the egg which she is going to lay; she must be able to choose the sex
of that egg so that each larva may obtain its proper portion of food.
Generally speaking, when the sexes are of different sizes, every
insect that collects food and prepares or selects a dwelling for its
offspring must be able to choose the sex of the egg in order to
satisfy without mistake the conditions imposed upon it.
The question remains how this optional assessment of the sexes is
effected. I know absolutely nothing about it. If I should ever learn
anything about this delicate point, I shall owe it to some happy
chance for which I must wait, or rather watch, patiently. Towards the
end of my investigations, I heard of a German theory which relates to
the Hive-bee and comes from Dzierzon, the apiarist. (Johann Dzierzon,
author of "Theorie und Praxis des neuen Bienenfreundes."--
Translator's Note.) If I understand it aright, according to the very
incomplete documents which I have before me, the egg, as it issues
from the ovary, is said already to possess a sex, which is always the
same; it is originally male; and it becomes female by fertilization.
The males are supposed to proceed from non-fertilized eggs, the
females from fertilized eggs. The Queen-bee would thus lay female
eggs or male eggs according as she fertilized them or not while they
were passing into her oviduct.
Coming from Germany, this theory cannot but inspire me with profound
distrust. As it has been given acceptance, with rash precipitancy, in
standard works, I will overcome my reluctance to devoting my
attention to Teutonic ideas and will submit it not to the test of
argument, which can always be met by an opposite argument, but to the
unanswerable test of facts.
For this optional fertilization, determining the sex, the mother's
organism requires a seminal reservoir which distils its drop of sperm
upon the egg contained in the oviduct and thus gives it a feminine
character, or else leaves it its original character, the male
character, by refusing it that baptism. This reservoir exists in the
Hive-bee. Do we find a similar organ in the other Hymenoptera,
whether honey-gatherers or hunters? The anatomical treatises are
either silent on this point or, without further enquiry, apply to the
order as a whole the data provided by the Hive-bee, however much she
differs from the mass of Hymenoptera owing to her social habits, her
sterile workers and especially her tremendous fertility, extending
over so long a period.
I at first doubted the universal presence of this spermatic
receptacle, having failed to find it under my scalpel in my former
investigations into the anatomy of the Sphex-wasps and some other
game-hunters. But this organ is so delicate and so small that it very
easily escapes the eye, especially when our attention is not
specially directed in search of it; and, even when we are looking for
it and it only, we do not always succeed in discovering it. We have
to find a globule attaining in many cases hardly as much as a
millimetre (About one-fiftieth of an inch.--Translator's Note.) in
diameter, a globule headed amidst a tangle of air-ducts and fatty
patches, of which it shares the colour, a dull white. Then again, the
merest slip of the forceps is enough to destroy it. My first
investigations, therefore, which concerned the reproductive apparatus
as a whole, might very well have allowed it to pass unperceived.
In order to know the rights of the matter once and for all, as the
anatomical treatises taught me nothing, I once more fixed my
microscope on its stand and rearranged my old dissecting-tank, an
ordinary tumbler with a cork disk covered with black satin. This
time, not without a certain strain on my eyes, which are already
growing tired, I succeeded in finding the said organ in the Bembex-
wasps, the Halicti (Cf. Chapters 12 to 14 of the present volume.--
Translator's Note.), the Carpenter-bees, the Bumble-bees, the
Andrenae (A species of Burrowing Bees.--Translator's Note.) and the
Megachiles. (Or Leaf-cutting Bees. Cf. Chapter 8 of the present
volume.--Translator's Note.) I failed in the case of the Osmiae, the
Chalicodomae and the Anthophorae. Is the organ really absent? Or was
there want of skill on my part? I lean towards want of skill and
admit that all the game-hunting and honey-gathering Hymenoptera
possess a seminal receptacle, which can be recognized by its
contents, a quantity of spiral spermatozoids whirling and twisting on
the slide of the microscope.
This organ once accepted, the German theory becomes applicable to all
the Bees and all the Wasps. When copulating, the female receives the
seminal fluid and holds it stored in her receptacle. From that
moment, the two procreating elements are present in the mother at one
and the same time: the female element, the ovule; and the male
element, the spermatozoid. At the egg-layer's will, the receptacle
bestows a tiny drop of its contents upon the matured ovule, when it
reaches the oviduct, and you have a female egg; or else it withholds
its spermatozoids and you have an egg that remains male, as it was at
first. I readily admit it: the theory is very simple, lucid and
seductive. But is it correct? That is another question.
One might begin by reproaching it with making a singular exception to
one of the most general rules. Which of us, casting his eyes over the
whole zoological progression, would dare to assert that the egg is
originally male and that it becomes female by fertilization? Do not
the two sexes both call for the assistance of the fertilizing
element? If there be one undoubted truth, it is certainly that. We
are, it is true, told very curious things about the Hive-bee. I will
not discuss them: this Bee stands too far outside the ordinary
limits; and then the facts asserted are far from being accepted by
everybody. But the non-social Bees and the predatory insects have
nothing special about their laying. Then why should they escape the
common rule, which requires that every living creature, male as well
as female, should come from a fertilized ovule? In its most solemn
act, that of procreation, life is one and uniform; what it does here
it does there and there and everywhere. What! The sporule of a scrap
of moss requires an antherozoid before it is fit to germinate; and
the ovule of a Scolia, that proud huntress, can dispense with the
equivalent in order to hatch and produce a male? These new-fangled
theories seem to me to have very little value.
One might also bring forward the case of the Three-pronged Osmia, who
distributes the two sexes without any order in the hollow of her
reed. What singular whim is the mother obeying when, without decisive
motive, she opens her seminal phial at haphazard to anoint a female
egg, or else keeps it closed, also at haphazard, to allow a male egg
to pass unfertilized? I could imagine impregnation being given or
withheld for periods of some duration; but I cannot understand
impregnation and non-impregnation following upon each other anyhow,
in any sort of order, or rather with no order it all. The mother has
just fertilized an egg. Why should she refuse to fertilize the next,
when neither the provisions nor the lodgings differ in the smallest
respect from the previous provisions and lodgings? These capricious
alternations, so unreasonable and so exceedingly erratic, are
scarcely appropriate to an act of such importance.
But I promised not to argue and I find myself arguing. My reasoning
is too fine for dull wits. I will pass on and come to the brutal
fact, the real sledge-hammer blow.
Towards the end of the Bee's operations, in the first week of June,
the last acts of the Three-horned Osmia become so exceptionally
interesting that I made her the object of redoubled observation. The
swarm at this time is greatly reduced in numbers. I have still some
thirty laggards, who continue very busy, though their work is in
vain. I see some very conscientiously stopping up the entrance to a
tube or a Snail-shell in which they have laid nothing at all. Others
are closing the home after only building a few partitions, or even
mere attempts at partitions. Some are placing at the back of a new
gallery a pinch of pollen which will benefit nobody and then shutting
up the house with an earthen stopper as thick, as carefully made as
though the safety of a family depended on it. Born a worker, the
Osmia must die working. When her ovaries are exhausted, she spends
the remainder of her strength on useless works: partitions, plugs,
pollen-heaps, all destined to be left unemployed. The little animal
machine cannot bring itself to be inactive even when there is nothing
more to be done. It goes on working so that its last vibrations of
energy may be used up in fruitless labour. I commend these
aberrations to the staunch supporters of reasoning-powers in the
animal.
Before coming to these useless tasks, my laggards have laid their
last eggs, of which I know the exact cells, the exact dates. These
eggs, as far as the microscopes can tell, differ in no respect from
the others, the older ones. They have the same dimensions, the same
shape, the same glossiness, the same look of freshness. Nor are their
provisions in any way peculiar, being very well suited to the males,
who conclude the laying. And yet these last eggs do not hatch: they
wrinkle, fade and wither on the pile of food. In one case, I count
three or four sterile eggs among the last lot laid; in another, I
find two or only one. Elsewhere in the swarm, fertile eggs have been
laid right up to the end.
Those sterile eggs, stricken with death at the moment of their birth,
are too numerous to be ignored. Why do they not hatch like the other
eggs, which outwardly they resemble in every respect? They have
received the same attention from the mother and the same portion of
food. The searching microscope shows me nothing in them to explain
the fatal ending.
To the unprejudiced mind, the answer is obvious. Those eggs do not
hatch because they have not been fertilized. Any animal or vegetable
egg that had not received the life-giving impregnation would perish
in the same way. No other answer is possible. It is no use talking of
the distant period of the laying: eggs of the same period laid by
other mothers, eggs of the same date and likewise the final ones of a
laying, are perfectly fertile. Once more, they do not hatch because
they were not fertilized.
And why were they not fertilized? Because the seminal receptacle, so
tiny, so difficult to see that it sometimes escaped me despite all my
scrutiny, had exhausted its contents. The mothers in whom this
receptacle retained a remnant of sperm to the end had their last eggs
as fertile as the first; the others, whose seminal reservoir was
exhausted too soon, had their last-born stricken with death. All this
seems to me as clear as daylight.
If the unfertilized eggs perish without hatching, those which hatch
and produce males are therefore fertilized; and the German theory
falls to the ground.
Then what explanation shall I give of the wonderful facts which I
have set forth? Why, none, absolutely none. I do not explain facts, I
relate them. Growing daily more sceptical of the interpretations
suggested to me and more hesitating as to those which I may have to
suggest myself, the more I observe and experiment, the more clearly I
see rising out of the black mists of possibility an enormous note of
interrogation.
Dear insects, my study of you has sustained me and continues to
sustain me in my heaviest trials. I must take leave of you for
to-day. The ranks are thinning around me and the long hopes have
fled. Shall I be able to speak to you again? (This is the closing
paragraph of Volume 3 of the "Souvenirs entomologiques," of which the
author has lived to publish seven more volumes, containing over 2,500
pages and nearly 850,000 words.--Translator's Note.)
CHAPTER 6. INSTINCT AND DISCERNMENT.
The Pelopaeus (A Mason-wasp forming the subject of essays which have
not yet been published in English.--Translator's Note.) gives us a
very poor idea of her intellect when she plasters up the spot in the
wall where the nest which I have removed used to stand, when she
persists in cramming her cell with Spiders for the benefit of an egg
no longer there and when she dutifully closes a cell which my forceps
has left empty, extracting alike germ and provisions. The Mason-bees
(Cf. "The Mason-bees": chapter 7.--Translator's Note.), the
caterpillar of the Great Peacock Moth (Cf. "Social Life in the Insect
World" by J.H. Fabre, translated by Bernard Miall: chapter 14.--
Translator's Note.) and many others, when subjected to similar tests,
are guilty of the same illogical behaviour: they continue, in the
normal order, their series of industrious actions, though an accident
has now rendered them all useless. Just like millstones unable to
cease revolving though there be no corn left to grind, let them once
be given the compelling power and they will continue to perform their
task despite its futility. Are they then machines? Far be it from me
to think anything so foolish.
It is impossible to make definite progress on the shifting sands of
contradictory facts: each step in our interpretation may find us
embogged. And yet these facts speak so loudly that I do not hesitate
to translate their evidence as I understand it. In insect mentality,
we have to distinguish two very different domains. One of these is
INSTINCT properly so called, the unconscious impulse that presides
over the most wonderful part of what the creature achieves. Where
experience and imitation are of absolutely no avail, instinct lays
down its inflexible law. It is instinct and instinct alone that makes
the mother build for a family which she will never see; that counsels
the storing of provisions for the unknown offspring; that directs the
sting towards the nerve-centres of the prey and skilfully paralyses
it, so that the game may keep good; that instigates, in fine, a host
of actions wherein shrewd reason and consummate science would have
their part, were the creature acting through discernment.
This faculty is perfect of its kind from the outset, otherwise the
insect would have no posterity. Time adds nothing to it and takes
nothing from it. Such as it was for a definite species, such it is
to-day and such it will remain, perhaps the most settled zoological
characteristic of them all. It is not free nor conscious in its
practice, any more than is the faculty of the stomach for digestion
or that of the heart for pulsation. The phases of its operations are
predetermined, necessarily entailed one by another; they suggest a
system of clock-work wherein one wheel set in motion brings about the
movement of the next. This is the mechanical side of the insect, the
fatum, the only thing which is able to explain the monstrous
illogicality of a Pelopaeus when misled by my artifices. Is the Lamb
when it first grips the teat a free and conscious agent, capable of
improvement in its difficult art of taking nourishment? The insect is
no more capable of improvement in its art, more difficult still, of
giving nourishment.
But, with its hide-bound science ignorant of itself, pure insect, if
it stood alone, would leave the insect unarmed in the perpetual
conflict of circumstances. No two moments in time are identical;
though the background remain the same, the details change; the
unexpected rises on every side. In this bewildering confusion, a
guide is needed to seek, accept, refuse and select; to show
preference for this and indifference to that; to turn to account, in
short, anything useful that occasion may offer. This guide the insect
undoubtedly possesses, to a very manifest degree. It is the second
province of its mentality. Here it is conscious and capable of
improvement by experience. I dare not speak of this rudimentary
faculty as intelligence, which is too exalted a title: I will call it
DISCERNMENT. The insect, in exercising its highest gifts, discerns,
differentiates between one thing and another, within the sphere of
its business, of course; and that is about all.
As long as we confound acts of pure instinct and acts of discernment
under the same head, we shall fall back into those endless
discussions which embitter controversy without bringing us one step
nearer to the solution of the problem. Is the insect conscious of
what it does? Yes and no. No, if its action is in the province of
instinct; yes, if the action is in that of discernment. Are the
habits of an insect capable of modification? No, decidedly not, if
the habit in question belongs to the province of instinct; yes, if it
belongs to that of discernment. Let us state this fundamental
distinction more precisely by the aid of a few examples.
The Pelopaeus builds her cells with earth already softened, with mud.
Here we have instinct, the unalterable characteristic of the worker.
She has always built in this way and always will. The passing ages
will never teach her, neither the struggle for life nor the law of
selection will ever induce her to imitate the Mason-bee and collect
dry dust for her mortar. This mud nest needs a shelter against the
rain. The hiding-place under a stone suffices at first. But should
she find something better, the potter takes possession of that
something better and instals herself in the home of man. (The
Pelopaeus builds in the fire-places of houses.--Translator's Note.)
There we have discernment, the source of some sort of capacity for
improvement.
The Pelopaeus supplies her larvae with provisions in the form of
Spiders. There you have instinct. The climate, the longitude or
latitude, the changing seasons, the abundance or scarcity of game
introduce no modification into this diet, though the larva shows
itself satisfied with other fare provided by myself. Its forebears
were brought up on Spiders; their descendants consumed similar food;
and their posterity again will know no other. Not a single
circumstance, however favourable, will ever persuade the Pelopaeus
that young Crickets, for instance, are as good as Spiders and that
her family would accept them gladly. Instinct binds her down to the
national diet.
But, should the Epeira (The Weaving or Garden Spider. Cf. "The Life
of the Spider" by J. Henri Fabre translated by Alexander Teixeira de
Mattos; chapters 9 to 14 and appendix.--Translator's Note.), the
favourite prey, be lacking, must the Pelopaeus therefore give up
foraging? She will stock her warehouses all the same, because any
Spider suits her. There you have discernment, whose elasticity makes
up, in certain circumstances, for the too-great rigidity of instinct.
Amid the innumerable variety of game, the huntress is able to discern
between what is Spider and what is not; and, in this way, she is
always prepared to supply her family, without quitting the domain of
her instinct.
The Hairy Ammophila gives her larva a single caterpillar, a large
one, paralysed by as many pricks of her sting as it has nervous
centres in its thorax and abdomen. Her surgical skill in subduing the
monster is instinct displayed in a form which makes short work of any
inclination to see in it an acquired habit. In an art that can leave
no one to practise it in the future unless that one be perfect at the
outset, of what avail are happy chances, atavistic tendencies, the
mellowing hand of time? But the grey caterpillar, sacrificed one day,
may be succeeded on another day by a green, yellow or striped
caterpillar. There you have discernment, which is quite capable of
recognizing the regulation prey under very diverse garbs.
The Megachiles build their honey-jars with disks cut out of leaves;
certain Anthidia make felted cotton wallets; others fashion pots out
of resin. There you have instinct. Will any rash mind ever conceive
the singular idea that the Leaf-cutter might very well have started
working in cotton, that the cotton-wool-worker once thought or will
one day think of cutting disks out of the leaves of the lilac- and
the rose-tree, that the resin-kneader began with clay? Who would dare
to indulge in any such theories? Each Bee has her art, her medium, to
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