48 BULLETIN 597, U. S. DEPARTMENT OF AGRICULTURE. 
deposited eggs it would probably prevent development of the embryo, 
as is the case with hens’ eggs during incubation; but even a test of 
this kind was onty slightly effective. 
A 2 per cent nicotine-sulphate solution was only partially effective. 
Nitrobenzine gas, which has recently been brought to our attention 
as a fumigant for external parasites of animals by Prof. William 
Moore, of the University of Minnesota, yielded good results at 25, 
24, and 10 hours’ exposure, but only a small percentage was killed 
at 4 hours. The fumigation was conducted in a common glass fruit 
jar into which a strip of cloth, impregnated with a few drops of 
nitrobenzine, was suspended. 
The phenol compounds, by a contact application, seem to be most 
effective in destroying young larve and preventing the further de- 
velopment of embryos. It will be observed that carbolic acid con- 
taining 2 per cent phenol yielded as good results as higher per- 
centages, and that this substance was most effectively used. 
With carbolic acid as a wash it will be well to be cautious of its 
effects upon the hands. If used at too great strength, the exposed 
skin of the hand will become white and peel off, although it does 
not affect the skin of the horse, which is protected by the hair. 
SUMMARY. 
Three species of horse bots—the common bot-fly (Gastrophilus 
intestinalis), the throat bot-fly (G. nasalis), and the nose fly (G. hae- 
morrhoidalis)—occur in the United States, and each is a source of 
considerable injury to horses. This injury is produced through 
worriment caused by the flies at the time the eggs are laid and by the 
attachment of the larvee, or bots, in the alimentary tract. 
Gastrophilus intestinalis and G. nasalis are widely distributed in 
the United States but G. haemorrhoidalis is confined to the North- 
Central and northern Rocky Mountain States. 
The nose fly (G. haemorrhoidalis) is by far the most annoying to 
horses at the time its eggs are laid. The adults appear early in June 
and reach the maximum of abundance during the first half of the 
season, disappearing with killing frosts. The eggs are deposited on the 
minute hairs on the iips, and those near the edges which are kept moist 
and receive friction hatch in from 5 to 10 days. The larve are taken 
in with food or water and attach themselves to the walls of the 
stomach. Here they remain until the following winter or spring 
and then migrate to the rectum, where they reattach. Before leaving 
the host they usually attach close to the anus and protrude from it. 
They remain in this position from 40 to 71 hours. After dropping 
to the ground the bots seek protection and pupate in from 18 to 170 
hours later. The pupa stage lasts from 21 to 68 days. The adults are 
