DIPTERA 



51 



Other pests closely related to the Hessian fly are the 

 wheat midge, feeding upon the kernels of grain, the clover- 

 seed midge, whose larvse destroy the growing seed of the 

 clover, and the pear midge, feeding in young pears. 



Though the word "Diptera" signifies two wings, yet 

 there are a few members of the order like the fleas which 

 have lost their wings 

 because of their par- 

 asitic habits. The 

 sheep tick dwelling 

 in the wool of the 

 sheep, the louse par- 

 asite on the honey 

 bee are also exam- 

 ples of wingless flies. 



Nearly all of the 

 Diptera have a com- 

 plete metamorphosis, i.e., exhibit four stages in their life 

 history. Most species deposit eggs, but a few, such as the 

 flesh flies, bring forth their young alive. The larva in this 

 order is an active wormlike creature which in some species, 

 such as the mosquito, buffalo gnat, and horse flies, dwells 

 in the water, while in others it lives in decaying matter or 

 is parasitic in plants or animals. The larva sheds its skin 

 (molts) two or more times, and usually the skin shed last 

 forms a kind of case in which transformation to pupa and 

 from pupa to adult occurs. The life of the adult insects 

 of this order is seldom longer than a few weeks, but some 

 species such as the house fly and certain mosquitoes live 

 in a dormant state for several months during the cold 

 season and become active in the spring. 



FIG. 31. Common dog or cat flea (Pulex serrati- 

 ceps). Photograph, enlarged thirty diameters. 



