12 
on or in the ground, or in the rejectamenta with which 
it has been removed, and there it turns to a chrysalis,—a 
very important point to notice with regard to methods of 
prevention. 
The change to the chrysalis, as with very many of the 
crop flies which we have often spoken of, the Mangold 
Fly for example, takes place by the maggot-skin harden¬ 
ing and drawing up into a barrel-shaped red-brown husk, 
within which the Fly developes, and from which it comes 
out after a period of a few weeks; rather less than six 
weeks is the longest time I see mentioned in ordinary 
circumstances. 
This is a short history of the Great Horse Bot Fly 
through all its stages: now, looking at its likings and 
dislikings (for practical use), we find it noticed to have 
such a strong preference for sunshine, warmth, and open 
air, and such an aversion to cold and presence of water, 
that I give the passage from Bracy Clark’s essay on the 
subject with little abridgement. He says :— “ The 
perfect Fly but ill sustains the changes of weather, and 
cold and moisture to any considerable degree would pro¬ 
bably prove fatal to it. 
“It is remarkable that these Flies never pursue the 
horse into the water. This aversion, I imagine, arises 
from the chilliness of that element, which is probably 
felt more exquisitely by them from the high temperature 
they had been exposed to during their larval state in the 
body of the animal. 
“ This change, if suddenly applied, would be fatal to 
them, but they are prepared for it by suffering its first 
effects in the quiescent and less sensible state of a 
chrysalis ; I have often seen the Fly during the night 
time and in cold weather fold itself up with the head and 
tail nearly in contact, and lying apparently in a torpid 
state through the middle of the summer.” * 
From these points, added to the observations previously 
given, that “ the female only lays on horses out of doors, 
* ‘Essay on the Bots of Horses and other Animals,’ by Bracy 
Clark, F.L.S., pp. 28, 29. 
