PHYLUM ARTHROPODA 



357 



FIG. 291. Order DIPTERA. Mosquito, Culex pungens. a, adult female. 

 b, egg mass on surface of water, c, young hanging from surface of water. 

 (From Howard, Bui. 25, Bur. Ent., U. S. Dep't Agric.) 



many lay eggs in plant tissue whose larvae when hatched cause an 

 abnormal growth called a gall, e.g. the pine-cone willowgall. One 

 gall-gnat, the Hessian fly, Cecidomyia destructor (Fig. 292), causes 

 a loss of about $10,000,000 annually to the wheat crop in this 

 country. Several species of this 

 family are paedogenetic (see p. 80). 

 The midges (CHIRONOMID.E) are 

 harmless little insects resembling 

 mosquitoes. The larvae of some 

 of them are the blood-red little 

 worms found in water. The black 

 flies (SIMULIID^E) are notorious 

 blood-sucking pests and the special 

 torment of hunters, fishermen, and 

 campers. Their larva: live in swift FIG 2Q2 . _ Order DIPTERA . 



Streams clinging to the surfaces of Hessian fly, Cecidomyia destructor. 



rocks, and the adults are therefore a ' larva ; b pup . a - ^ om D , a y i en - 



. port, after Standard Natural His- 



found in the vicinity of water. tory.) 



