PHYLUM ARTHROPOD A 



351 



Fig. 291. — Order Diptera. Mosquito, C-ulex 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 (seep. 80). 



The midges (Chironomid^) are 



harmless little insects resembling 



mosquitoes. The larvae of some 



of them are the blood-red little 



worms found in water. The black 



flies (SiMULiiDiE) are notorious 



blood-sucking pests and the special 



torment of hunters, fishermen, and 



campers. Their larvae live in swift 



1 < Fig. 292. — Order Diptera. 



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



rocks, and the adults are therefore a ' larva f ; b - pup . a - , ( !J° m ^ n ' 



port, after Standard Natural His- 



found in the vicinity of water. tory.) 



