244 ELEMENTARY ZOOLOGY. 



in their habits. When the young are hatched they are 

 much like the adult. They grow and undergo the slight 

 changes necessary, by a series of moults in which the 

 hard outer shell is shed. The soft parts then grow before 

 the new shell hardens. 



This order is of considerable economic importance. 

 The locusts are active feeders, multiply abundantly, and 

 often move in great swarms in search of food. In this 

 way the Rocky Mountain locust swept down from its 

 breeding places over the plains of Nebraska and Kan- 

 sas in 1873 an< ^ again in 1878, stripping the fields of 

 vegetation. 



261. The Diptera (House-flies, Horse-flies, Mosquitoes, 

 Gnats, etc.) (Fig. 91). This group has only one pair of 

 wings (whence the name), and the mouth parts are 

 adapted to piercing and sucking instead of biting. There 

 are a great many species in this order and they have 

 extraordinary powers of reproduction. The eggs are 

 laid and the larvae develop in connection with decaying 

 organic matter, as flesh, fruit, manure, stagnant water, 

 and the like. The larva? of flies .are known as mag- 

 gots; those of mosquitoes and gnats are the "wiggle- 

 tails" of the rain barrel or the pond. These animals do 

 their growing in the larval stage and pass into the mature 

 stage full grown. The members of this group are very 

 important to man. While the larvae are scavengers and 

 consume decaying matter, the adults are unquestionably 

 among the worst carriers of disease known to us. The 

 work of the mosquito in this respect has already been 

 referred to (p. 160). The common house-fly is prob- 

 ably as great an offender in spreading typhoid and other 

 similar intestinal diseases, by carrying the germs and 



