INSECTS AS PARASITES 191 
other animals during the early part of their existence, as, eg., 
the Bot-Flies (@strzdz), 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 larva, 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 
T 2 3 4 5 6 
Fig. 1136.—Horse-Bot (Gastvophilus equi). 1, 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 “bot”. Its powers of adhesion 
are considerably increased by the presence of circlets of short 
spines on the body. When a large number of these larve 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 (Gstrus ovis) are developed 
internally, and the female fly deposits the just-born larve 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 
