INSECTS AS PARASITES 191 



other animals during the early part of their existence, as, e.g., 

 the Bot- Flies (CEstridtz), which are only too well known to the 

 owners of stock. The mouth of the adult is greatly reduced, so 

 that there is no question of blood-sucking, while the larvae do not 

 devour the living substance of their hosts, but absorb the fluid 

 which surrounds them, and is generally a morbid product result- 

 ing from the irritation due to their presence. The Horse- Bot 

 (Gastrophilus equi, fig. 1136) lays her eggs upon those parts of 

 the horse's body which are easily reached by the tongue, and 

 the young larvae, when they hatch out, are thus conveyed to 

 the mouth, whence they make their way to the stomach. The 

 head of the maggot is provided with hooks by which it bores 

 into the lining of that organ. In later stages it becomes ovoid 



Fig. 1136. Horse-Bot (Gastrophilus equt). i, Male; 2, female; 3, egg (much enlarged) attached 

 to hair; 4, young larva (enlarged); 5, older larva; 6, empty pupa-case. 



in shape, and is known as a "hot". Its powers of adhesion 

 are considerably increased by the presence of circlets of short 

 spines on the body. When a large number of these larvae are 

 present they set up inflammation, &c., sometimes with fatal 

 results, and they have even been known to bore right through 

 the wall of the stomach. After about nine or ten months the 

 larva looses its hold, and is carried through the digestive organs 

 of the horse to the exterior, where it passes into the motionless 

 pupa stage, from which the adult fly later on emerges. 



The eggs of the Sheep -Bot (CEstrus ovis] are developed 

 internally, and the female fly deposits the just -born larvae near 

 the nostrils of the sheep. Thence they pass into the nose, and 

 ultimately into spaces (frontal sinuses) in the bones of the head, 

 where they become " bots ". After some nine months' growth 

 these make their way back into the nose, from which they appear 

 to be sneezed out, and pass into the pupa stage. One or two 

 more pests of the kind will be dealt with later, in the section on 

 ANIMAL FOES. 



Before leaving the order of Flies, it may be noted that the 



