hollowed by another. This is the case with Tripoxylon figulus. To
obtain the store-rooms wherein to deposit her scanty stock of
Spiders, she divides her borrowed cylinder into very unequal cells,
by means of slender clay partitions. Some are a centimetre (.39
inch.--Translator's Note.) deep, the proper size for the insect;
others are as much as two inches. These spacious rooms, out of all
proportion to the occupier, reveal the reckless extravagance of a
casual proprietress whose title-deeds have cost her nothing.

But, whether they be the original builders or labourers touching up
the work of others, they all alike have their parasites, who
constitute the third class of bramble-dwellers. These have neither
galleries to excavate nor victuals to provide; they lay their egg in
a strange cell; and their grub feeds either on the provisions of the
lawful owner's larva or on that larva itself.

At the head of this population, as regards both the finish and the
magnitude of the structure, stands the Three-pronged Osmia (Osmia
tridentata, DUF. and PER.), to whom this chapter shall be specially
devoted. Her gallery, which has the diameter of a lead pencil,
sometimes descends to a depth of twenty inches. It is at first almost
exactly cylindrical; but, in the course of the victualling, changes
occur which modify it slightly at geometrically determined distances.
The work of boring possesses no great interest. In the month of July,
we see the insect, perched on a bramble-stump, attack the pith and
dig itself a well. When this is deep enough, the Osmia goes down,
tears off a few particles of pith and comes up again to fling her
load outside. This monotonous labour continues until the Bee deems
the gallery long enough, or until, as often happens, she finds
herself stopped by an impassable knot.