46 AN ACCOUNT 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. fini the last segment was considered to 
be stigmate, but this is not the case, the last segment being hidden 
under the eighth. 
The larvee 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 larvae 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 larvze 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 
Fic. 10.—The Anchor Process of (1) Hessian Fly (C. destructor) and (2) of Wheat 
Midge (VL. ¢ré¢icz), (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 larvee only may be found, as in certain willow galls (C. clau- 
stlia on Salix alba). 
There are certain larvze 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 Chelidonium 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. Thelarva 
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 sub-genus Diflosis, to which C. #zgra most 
probably belongs. 
