Bramble-Bees and Others | Page 9

impossible in either direction.
These surmises accord with the facts: the chronological sequence of the
cells tells us nothing about the chronological sequence of the hatchings,
which take place without any definite order. There is, therefore, no
surrender of rights of primogeniture, as Leon Dufour thought: each

insect, regardless of the others, bursts its cocoon when its time comes;
and this time is determined by causes which escape our notice and
which, no doubt, depend upon the potentialities of the egg itself. It is
the case with the other bramble-dwellers which I have subjected to the
same test (Osmia detrita, Anthidium scapulare, Solenius vagus, etc.);
and it must also be the case with Odynerus rubicola: so the most
striking analogies inform us. Therefore the singular exception which
made such an impression on Dufour's mind is a sheer logical illusion.
An error removed is tantamount to a truth gained; and yet, if it were to
end here, the result of my experiment would possess but slight value.
After destruction, let us turn to construction; and perhaps we shall find
the wherewithal to compensate us for an illusion lost. Let us begin by
watching the exit.
The first Osmia to leave her cocoon, no matter what place she occupies
in the series, forthwith attacks the ceiling separating her from the floor
above. She cuts a fairly clean hole in it, shaped like a truncate cone,
having its larger base on the side where the Bee is and its smaller base
opposite. This conformation of the exit-door is a characteristic of the
work. When the insect tries to attack the diaphragm, it first digs more
or less at random; then, as the boring progresses, the action is
concentrated upon an area which narrows until it presents no more than
just the necessary passage. Nor is the cone-shaped aperture special to
the Osmia: I have seen it made by the other bramble-dwellers through
my thick disks of sorghum-pith. Under natural conditions, the partitions,
which, for that matter, are very thin, are destroyed absolutely, for the
contraction of the cell at the top leaves barely the width which the
insect needs. The truncate, cone-shaped breach has often been of great
use to me. Its wide base made it possible for me, without being present
at the work, to judge which of the two neighbouring Osmiae had
pierced the partition; it told me the direction of a nocturnal migration
which I had been unable to witness.
The first-hatched Osmia, wherever she may be, has made a hole in her
ceiling. She is now in the presence of the next cocoon, with her head at
the opening of the hole. In front of her sister's cradle, she usually stops,
consumed with shyness; she draws back into her cell, flounders among
the shreds of the cocoon and the wreckage of the ruined ceiling; she
waits a day, two days, three days, more if necessary. Should impatience

gain the upper hand, she tries to slip between the wall of the tunnel and
the cocoon that blocks the way. She even undertakes the laborious
work of gnawing at the wall, so as to widen the interval, if possible. We
find these attempts, in the shaft of a bramble, at places where the pith is
removed down to the very wood, where the wood itself is gnawed to
some depth. I need hardly say that, although these lateral inroads are
perceptible after the event, they escape the eye at the moment when
they are being made.
If we would witness them, we must slightly modify the glass apparatus.
I line the inside of the tube with a thick piece of whity- brown
packing-paper, but only over one half of the circumference; the other
half is left bare, so that I may watch the Osmia's attempts. Well, the
captive insect fiercely attacks this lining, which to its eyes represents
the pithy layer of its usual abode; it tears it away by tiny particles and
strives to cut itself a road between the cocoon and the glass wall. The
males, who are a little smaller, have a better chance of success than the
females. Flattening themselves, making themselves thin, slightly
spoiling the shape of the cocoon, which, however, thanks to its
elasticity, soon recovers its first condition, they slip through the narrow
passage and reach the next cell. The females, when in a hurry to get out,
do as much, if they find the tube at all amenable to the process. But no
sooner is the first partition passed than a second presents itself. This is
pierced in its turn. In the same way will the third be pierced and others
after that, if the insect can manage them, as long as its strength holds
out. Too weak for these repeated borings, the males do