46 A N ACCO UNT OF BRITISH FLIES. 



and position. One pair on the first thoracic, and eight on the first 

 eight abdominal segments, the last segment being devoid of any 

 stigmatic opening. In C. pini the last segment was considered to 

 be stigmate, but this is not the case, the last segment being hidden 

 under the eighth. 



The larva; may be hairy or armed with bristles, and may have 

 fleshy caruncles along the back, or may be entirely smooth. The 

 last segment may be armed with two curved processes, which are 

 used in leaping, several of these larvce being noted for their saltatorial 

 habits (C nigra).* They are often very active, and this has been 

 particularly noticed in rainy weather, and also during and after a 

 thunderstorm. 



The larva; may also have pseudopods on their ventral surface. They 

 do not seem to require much nourishment, moisture being essential 

 to them. They produce the galls through some irritating function 



Fig. io. — The Anchor Process of (i) Hessian Fly (C. destructor) and (2) of Wheat 

 Midge (Z>. tritici), (from Miss Ormerod's manual). 



peculiar to them, causing an abnormal flow of sap. Some species 

 are seen, however, to be extremely voracious. They are generally 

 found in companies ; as many as eight or ten may often be got from 

 the galled flower spikes in which many live ; on the other hand, 

 single larva; only may be found, as in certain willow galls (C. dau- 

 silia on Salix alba). 



There are certain larvje that live as " guests " in the galls of other 

 species ; whether these live upon the excreta of their companions or 

 upon the sap is not definitely known. The same applies to species that 

 live under bark; they may live upon the excrements of other insects. 



M. Vallot mentions some that live upon Acari, sucking their 

 juices, and found under the leaves of Chelidonhmi majus. At the 

 close of larval life the maggots may leave the galls and pupate in 

 the earth ; but some species remain and pass the dormant stage in 

 their old homes. The lives of the maggots vary in length. The larva 

 of the Hessian-fly (C. destructor), according to Dr. Lindeman, lives 

 twenty-eight days, and then changes at the spot where it fed to a 



* This is a character of the subgenus Diplosis, to which C. nigra most 

 }; probably belongs. 



