Bramble-Bees and Others | Page 8

stump of bramble. The operation is
performed in winter. The larvae, at that time, have long been enveloped
in their silken case. To separate the cocoons from one another, I
employ artificial partitions consisting of little round disks of sorghum,
or Indian millet, about half a centimetre thick. (About one-fifth of an
inch.--Translator's Note.) This is a white pith, divested of its fibrous
wrapper and easy for the Osmia's mandibles to attack. My diaphragms
are much thicker than the natural partitions; this is an advantage, as we
shall see. In any case, I could not well use thinner ones, for these disks
must be able to withstand the pressure of the rammer which places
them in position in the tube. On the other hand, the experiment showed
me that the Osmia makes short work of the material when it is a case of
drilling a hole through it.
To keep out the light, which would disturb my insects destined to spend
their larval life in complete darkness, I cover the tube with a thick
paper sheath, easy to remove and replace when the time comes for
observation. Lastly, the tubes thus prepared and containing either
Osmiae or other bramble-dwellers are hung vertically, with the opening
at the top, in a snug corner of my study. Each of these appliances fulfils
the natural conditions pretty satisfactorily: the cocoons from the same
bramble-stick are stacked in the same order which they occupied in the
native shaft, the oldest at the bottom of the tube and the youngest close
to the orifice; they are isolated by means of partitions; they are placed
vertically, head upwards; moreover, my device has the advantage of
substituting for the opaque wall of the bramble a transparent wall
which will enable me to follow the hatching day by day, at any moment
which I think opportune.
The male Osmia splits his cocoon at the end of June and the female at
the beginning of July. When this time comes, we must redouble our
watch and inspect the tubes several times a day if we would obtain
exact statistics of the births. Well, during the six years that I have
studied this question, I have seen and seen again, ad nauseam; and I am
in a position to declare that there is no order governing the sequence of
hatchings, absolutely none. The first cocoon to burst may be the one at
the bottom of the tube, the one at the top, the one in the middle or in

any other part, indifferently. The second to be split may adjoin the first
or it may be removed from it by a number of spaces, either above or
below. Sometimes several hatchings occur on the same day, within the
same hour, some farther back in the row of cells, some farther forward;
and this without any apparent reason for the simultaneity. In short, the
hatchings follow upon one another, I will not say haphazard--for each
of them has its appointed place in time, determined by impenetrable
causes--but at any rate contrary to our calculations, based on this or the
other consideration.
Had we not been deceived by our too shallow logic, we might have
foreseen this result. The eggs are laid in their respective cells at
intervals of a few days, of a few hours. How can this slight difference
in age affect the total evolution, which lasts a year? Mathematical
accuracy has nothing to do with the case. Each germ, each grub has its
individual energy, determined we know not how and varying in each
germ or grub. This excess of vitality belongs to the egg before it leaves
the ovary. Might it not, at the moment of hatching, be the cause why
this or that larva takes precedence of its elders or its juniors,
chronology being altogether a secondary consideration? When the hen
sits upon her eggs, is the oldest always the first to hatch? In the same
way, the oldest larva, lodged in the bottom storey, need not necessarily
reach the perfect state first.
A second argument, had we reflected more deeply on the matter, would
have shaken our faith in any strict mathematical sequence. The same
brood forming the string of cocoons in a bramble-stem contains both
males and females; and the two sexes are divided in the series
indiscriminately. Now it is the rule among the Bees for the males to
issue from the cocoon a little earlier than the females. In the case of the
Three-pronged Osmia, the male has about a week's start. Consequently,
in a populous gallery, there is always a certain number of males, who
are hatched seven or eight days before the females and who are
distributed here and there over the series. This would be enough to
make any regular hatching-sequence