102 SOCIAL HABITATIONS. 
is sometimes hatched at the same time with that of the 
bee, but generally later. In the first instance, the larva 
feeds on the provisions which were supplied for the bee, 
and so starves the poor creature to death; and in the 
latter case, it is not hatched until the young bee is large 
and fat, and capable of affording ample subsistence to 
the parasite, which fastens upon it and devours all the 
softer portions. 
Then there are the Cuckoo FLiEs, which bear some 
resemblance to the common house-fly, but which are 
parasitic, feeding on the larve of other insects, and 
selecting the same species which are persecuted by the 
firetails. When the Tachina larva hag eaten that of the 
mason bee, it forms an oval cocoon, and there remains 
until the time for becoming a perfect insect. A single 
larva of the mason bee seems to be sufficient for the 
Tachina grub, as Mr. Rennie has recorded an instance 
where tivo larvee of the mason bee were in a nest into 
which a single egg of a Tachina had been introduced. 
The parasitic larva devoured one of the rightful inhabi- 
tants, but did not touch the other, and the cocoons of 
the bee and the Tachina were formed side by side. 
Sometimes, as has already been mentioned, the chry- 
salis itself of a lepidopterous insect becomes the home of 
the parasite. Ihave found the pups of various butter- 
flies absolutely filled with tiny ichneumon flies of the 
most brilliant colours; and in the British Museum there 
is an excellent example of a chrysalis, which has been 
filled by a single ichneumon fly, of such a size that the 
little chrysalis from which it was taken seems scarcely 
capable of holding it and its cocoon. 
We now pass to a remarkable series of insects belong- 
