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.