PAKASITIC INSECTS, 481 



Those splendid insects which are popularly called Euby- 

 TAILED Flies, or Fieetails, and scientifically are termed Chry- 

 sididce, are also to be ntunbered among the parasitic insects. 



They make no nests for themselves, but intrude upon those of 

 various mason and mining bees, and several other insects. The 

 Firetail does not, however, lay its eggs in the body of the larva, 

 but makes its way into the nest while the rightful owner is 

 absent, and places an egg near that of the bee. The egg of the 

 parasite is sometimes hatched at the same time with that of the 

 bee, but generally later. In the first instance, the larva feeds on 

 the proAdsions 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 after portions. 



Then there are the Cuckoo Flies (Tachince), which bear some 

 resemblance to the common house-fly, but which are parasitic, 

 feeding on the larvae of other insects, and selecting the same 

 species which are persecuted by the fixetails. When the Tachina 

 larva has 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 sufKcient for the 

 Tachina grub, as Mr. Eennie has recorded an instance where two 

 larvae of the mason l)ee were in a nest into which a single egg 

 of a Tachina had been introduced. The parasitic larva de- 

 voured one of the rightful inhabitants, 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 chrysalis itself 

 of a lepidopterous insect becomes the home of the parasite. 

 I have found the pupae of various butterflies absolutely iUled 

 with tiny ichneumon flies of the most brilliant colours ; and in 

 the British Museum there is an excellent example of a chrysalis, 

 which has b«en 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 belonging to 

 the same order as the ichneumons, but parasitic upon vegetables 



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