THE INSECT WORLD. 



little family ConopidcB, which is not at all injurious, but rather 

 the contrary. Professor Comstock calls them "thick-head flies," 

 and the term is not bad, because the head is usually very promi- 

 nent and as wide or wider than the body. The thorax is unusu- 

 ally short, and bears a long abdomen having the 

 basal joints very slender and the terminal joints Fig- 403- 

 enlarged, bulb-like, much resembling in appear- 

 ance that of certain wasps. The flies are moder- 

 ate in size, with the wings more or less brown or 

 clouded, and they may often be found on flowers 

 after midsummer, in company with the Hymen- 

 optera, which they resemble. The larvae are 

 parasites, chiefly, it is said, upon bumble-bees and wasps, in 

 which case they are not beneficial ; but also on grasshoppers, in 

 which respect they deserve our most distinguished consideration. 



Distinctly injurious insects we find in the family CEstridce, or 

 "bot-flies." These are usually of good size, sometimes even 

 very large, and peculiar by having the mouth parts almost 

 entirely aborted. Some of the species are very hairy, yellowish 

 in color, and with rather a pointed abdomen ; while others are 

 very plump, robust flies, blue or blue-black in color, often with 

 a whitish bloom like that of a plum, formidable in appearance, 

 though in fact entirely inoffensive in this stage. In the larval 

 condition they are known as "bots," and live beneath the skin, 

 in the intestines, or in the mucus-lined head passages of the 

 animals infested by them. Thus, the "horse-bot," Gastrophilus 

 equi, passes its Hfe in the stomach, attached to the inner coat, and 

 there remains until full grown, when it releases its hold and is 

 passed in the natural way through the anus. It then crawls into 

 some convenient place just below the surface of the ground, or 

 even among rubbish on top of it, and changes to a pupa. The 

 adult lays its eggs on the hair, chiefly of the forelegs, at points 

 easily reached by the tongue of the animal in licking itself. The 

 eggs are thus removed, carried into the mouth on the tongue, 

 and so into the stomach, where the larvae hatch almost immedi- 

 ately and at once attach themselves. It is readily seen that this 

 habit gives us a certain possibility of controlling the insects, 

 because if the horses can be prevented from licking off the eggs, 

 they never can reach the proper location for their growth. 



