22 8 ELEMENTARY ENTOMOLOGY 



Gall-gnats. The smallest and most deli- 

 cate of the gnatlike flies are the gall-gnats 

 (Cecidomyiidac). The adults are rarely 

 over one eighth of an inch long, with long 

 antennae clothed with short hairs, and with 

 the wing-veins greatly reduced in number. 

 They will be rarely noticed by the begin- 

 ner, but the work of the larvae is often 

 much in evidence, owing to their feeding 

 within the stems and leaves of plants and 

 giving rise to galls. Frequently a green, 

 cone-shaped gall is found on the tips of 

 willow twigs, known as the pine-cone 

 willow-gall, which is caused by one of 



FIG. 359. Pear midge (Di- . , .. ., x 



plosispyrivord). (Enlarged) these larvae (Cccidomyia strobiloides]. 



(After Riiey) The larvae of the clover-seed midge live in 



the heads of clover and destroy the seed 



so that in many sections it is often impossible to mature it. The 

 best-known exam- 

 ple of the family, 

 an d our worst wheat 

 pest, is the Hessian 

 fly, so called be- 

 cause it was sup- 

 posedly introduced 

 in straw brought 

 over to Long Is- 

 land by the Hes- 

 sian troops during 

 the Revolutionary 

 War. The mag- 

 gots bore into the 

 crown and stalks 

 of wheat, weaken- 

 ing the plant and 

 seriously curtailing 

 production where 



FIG. 360. The Hessian fly, adult male. (Much enlarged) 



they are abundant. (After Marlatt, United States Department of Agriculture) 



