CHEESE-FLY. 293 



ORDER VI. DIPTEROUS INSECTS. 



18. FLY TRIBE. 



The greater part of the Flies live on putrid or filthy 

 substances. Most of them are torpid during the winter. 



Flesh-fly. As soon as that change takes place in 

 animal substances, which approaches to putridity, these 

 insects collect upon them, and there deposit their nume- 

 rous offspring, in the shape of minute white grubs. When 

 these have attained their full growth, which is generally 

 in the course of seven or eight days, they quit their 

 food, and wander in search of loose earth or rubbish, 

 in which they bury themselves, and undergo their change, 

 first to pupae or chrysalids, and afterwards to perfect 

 insects. 



Cheese-fly. The grubs, or larvae, of these insects, 

 are well known in decayed cheese, by the name of hop- 

 pers. They proceed from eggs, which are deposited 

 by the parent Flies in the crevices of the cheese. The 

 powers of motion in the hoppers are very surprising. 

 One of them, which was not the fourth part of an inch 

 in length, has been known to leap out of a box six 

 inches deep, or to a height equal to more than twenty- 

 four times the length of its own body. A short time 

 previously to their change into chrysalids, they crawl 

 out of the cheese, and become stiff and lifeless. The fly 

 afterwards bursts out, through an opening in the skin 

 near the head. 



