THE GALL FLIES. 297 



is absent, and places an ^gg 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 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 {Tachhice), which bear 

 some resemblance to the common house-fly, but w^iich are pa- 

 rasitic, feeding on the larvae of other insects, and selecdng the 

 same species which are persecuted by the firetails. 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 sufficient 

 for the Tachina grub, as Mr. Rennie has recorded an instance 

 where two larvae 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 inhabitants, but did not 

 touch the other, and the cocoons of the bee and the Tachina 

 were formed side by side. 



We now pass to a remarkable series of insects belongmg 

 to the same order as the ichneumons, but parasitic upon vege- 

 tables and not on animals. Their scientific name is Cynipidce, 

 and they are popularly known as Gall Flies, because they 

 cause those singular excrescences which are so familiar to us 

 under the name of Galls. This group comprises a vast number 

 of species, all of which have a strong family resemblance, 

 though they greatly differ from each other in size, form, and 

 colour. 



In the accompanying illustration are given several examples 

 of British Galls, most of which are tolerably common in this 

 country, and some of which can be found in plenty. 



In the left hand upper corner of the illustration is a figure of 

 an oak-leaf, upon which are two globular projections. These 



