GASTROPHILUS HAEMORRHOIDALIS AND OTHER BOTS. 49 
very active, and as they deposit only one egg at a time they are not 
so frequently seen about horses as are the adults of the common bot- 
fly. They take no food in the adult stage. Their length of life is 
from 1 to 7 days. 
The throat bot-fly (G@. nasalis) deposits its eggs on the hairs under 
the jaws and to some extent on the shoulders and other parts of the 
host. The larvee of this species attach themselves to the walls of the 
pharynx and also to those of the stomach and duodenum. They do 
not reattach in the rectum or at the anus as do the bots of the nose 
fly. Pupation occurs in from 14 to 2 days after the larve have 
passed from the host, and adults emerge in from 20 to 56 days later. 
The adults are somewhat longer lived than those of the nose fly. 
The flies cause considerable annoyance to horses during oviposition 
but not as serious as in the case of the nose fly. 
The common bot-fly (@. intestinalis) usually appears later in the 
season than the nose fly and becomes most abundant just before kill- 
ing frosts. The eggs are deposited on all parts of the body, but 
preferably on the fore legs. They hatch upon the application of 
moisture and friction. From 9 to 11 days after oviposition appears 
to be the most favorable period for hatching, although some may 
hatch as early as 7 days and others as late as 96 days after oviposi- 
tion. The larve attach in any part of the stomach, but the last-stage 
bots are found mostly in the left sac. They continue to drop from 
the host for a long period of time. Pupation takes place in protected 
places on the surface of the soil and the pupa stage lasts from 40 to 
60 days. 
All Gastrophilus larve are surprisingly resistant to chemicals. 
The treatment of horses with carbon disulphid in three doses followed 
by a physic is satisfactory if administered in the late fall. Spring 
treatment is less effective, as the full-grown larve are more resistant, 
and many of the nose-fly bots have left the stomach and passed back 
to the rectum at that time. 
Larve of G. haemorrhoidalis may be removed from the rectum 
mechanically, but this is laborious. The use of enemas containing 
insecticides is ineffective. 
As a repellent, pine tar mixed with other material gave good re- 
sults against the common bot-fly and the throat bot-fly. Such mix- 
tures may be utilized to cause the flies to lay eggs on parts of the body 
less accessible to the horse’s mouth. 
Various nose protectors are in use against G. haemorrhoidalis, but 
there are objections to many of them. A piece of leather suspended 
below the lips from the bit rings is simplest and best. For animals 
on pasture a halter with a box-like arrangement and throat cover has 
been devised to protect horses against infeetation by all three species, 
