THE PSITHYRUS VESTALIS. 
253 
pellets crowded one over the other is observed, and these little 
things form the paste which is destined to nourish the future 
larvae. Mixed with them, and encircled with wax, there are either 
eggs, larvae, or cocoons, and at certain times of the year cups of ' 
wax, which contain a very pure honey, may be seen on the sides 
of the nest. The larvae resemble those of other bees, and they 
spin themselves cocoons, which are egg-shaped, and which are 
usually found pressed one against the other. They are of different 
dimensions — the smallest, always the most numerous, are the 
cocoons of workers ; those of medium size belong to males ; and 
the largest contain fertile females. Before getting out of the 
cocoons they have to be cut round at one end so that a portion 
comes off resembling a lid. 
In the accompanying engraving there are many workers of 
this bee, and a large female is represented on the ground on the 
right hand side. The cocoons are exposed to view. 
Another humble bee ( Bombus terreslris) is a very large kind, 
and forms its nests in the earth at a considerable depth. These 
bees do not use mosses, but make a lining to the roof of their 
dwelling with layers of wax. 
Formerly certain Hymenoptera were classed by all naturalists 
amongst the humble bees, and, indeed, a superficial examination 
of them permitted this to be done, for they have the same shape, 
size, and colours, and look like them ; but Lepeletier de Saint- 
Fargeau recognised them as parasites, and collected them under 
the genus Psithyrus. These insects which are so like the humble 
bees have only two kinds of individuals amongst them, for none of 
them are workers. There are males and females, and these have, 
as might be expected, no implements for working. Every species 
of humble bee has its parasite, its particular Psithyrus ; and 
curiously enough the parasite has the peculiar colouring of the in- 
sect it robs, and usually there is no difficulty in telling the habits 
of a Psithyrus by its shape and tints. There is something in this 
resemblance more than chance, for it will be found that some flies, 
not wasps or bees, but Diptera of the genus Volucella } which are 
parasites in the nests of humble bees and wasps, resemble their 
unwilling hosts in their colours. One of the commonest species 
of the genus Psithyrus ( Psithyrus vestalis) resembles the common 
