^20 



DIPTEEA OR TEUE FLIES. 



The laivaj mostly change in their old skin, which hardens and 

 forms a case or puparium. 



The Hessian Fly (Cbcidomyia destructor). 



In 1886 there was a great scare in Britain concerning this 

 pest, which was thought to have been introduced from America. 

 It was not, however, but is an undoubted native species. The 

 damage caused by this midge is very severe on the American 



B. 



Fni. 117. — A, Larva, and b, Pqe'A of a CtrUlomnin (grt'ntly enl.^lv'(^li). 



continent ; but here it only now and then makes itself suffi- 

 ciently noxious to call for special attention. The adult fly is a 

 small hairy creature, brownish in colour, with pinkish markings 

 on the abdomen in the female, much darker in the male. It 

 belongs to the genus O'cidomi/ia, which can be told by the 

 venation of the wings shown in ligure 119. The small reddish- 

 white cylindrical eggs are laid by tlie female in rows on the 



