THE GALL-GNATS 



(Family Cecidomyiida.) 



The minute flies of this family are small delicate flies some- 

 what resembling mosquitoes, but do not bite. The antennae are 

 many-jointed, and are furnished with whorls of hair. The wings 

 have only a few longitudinal veins and but a single cross vein in 

 some genera. The legs are not swollen, and the body and wings 

 are clothed with hairs which are easily rubbed off. 



In this country these flies have not been systematically 

 studied with great care. 

 There are many species, 

 however, and some of them 

 are known only by the 

 work of their larvae. About 

 one hundred species have 

 been described in the United 

 States. 



The larvae differ con- 

 siderably in their habits, but 

 most of them form galls on 

 the twigs or leaves of different plants. Some live under bark and 

 others (of the genus Diplosis) prey upon plant-lice and bark-lice. 

 Others still produce plant deformities of different kinds which 

 cannot strictly be called galls. 



The larvae are small, somewhat flattened maggots, tapering 

 at each end, and frequently brightly colored with some shade of 

 red or yellow. 



The pupa is either naked or is enclosed in a delicate silken 

 cocoon. 



The most famous member of this group is the so-called 

 Hessian fly (Cecidomyia destructor Say.) This species lives, in 



"3 



Fig. 63. Cecidomyia trifolii. 

 (After Comstock.) 



