PARASITES AND PARASITIC DISEASES 233 



horses harbor a few, some as many as two or three hundred (Fig. 

 67). 



The bots remain in the stomach for about ten months, or until 

 May or June, sucking blood for their sustenance. Then they loosen 

 their hold, pass along through the bowels with the ingesta, and 

 escape in the feces. If conditions are favorable they burrow into 

 the soil and form a pupa. Some four or six weeks are passed in 

 this stage, after which a perfect fly emerges ready to lay eggs. 



Many different remedies have been used to free horses from 

 bots, but all are of little or no value. Drugs strong enough to 



Fig. 67. — Bots attached to the lining of the stomach. P\ill-grown larva of the 

 Gastrophilus equi. (U. S. Dept. of Agric, Division of Entomology.) 



cause the bots to loosen their hold will injure the walls of the 

 stomach, so cannot be used. Bots seldom cause serious injury, 

 but may produce irritation and lack of thriftiness if present in 

 large numbers by interfering with gastric secretion. In view of the 

 fact that bots and many other internal parasites pass from the 

 host as soon as the animals are turned out in the spring, treatment 

 should be given in early winter to be effective. Prevention is 

 easiest and most satisfactory. Clip off all eggs found attached 

 to the hair with a sharp razor or destroy them by singeing with a 

 flame. 



