268 YEARBOOK OF THE DEPARTMENT OF AGRICULTURE. 
should be imraediateh^ dropped into the burrow, the mouth of which 
should then be closed. 
For introducing the bisulphide there is nothing better than dry 
horse manure — a material which costs nothing and is always at hand. 
A lump of horse manure Avet with the bisulphide and dropped into a 
hole falls at once to the bottom of the vertical part, as shown in the 
diagram (tig. 25, J), where it is very near the animals. The liquid 
can be used to best advantage after a rain, w^hen the interspaces in the 
soil are filled with water, so that the fumes are less readil}^ difi'used 
into the surrounding ground. This, however, is of much Jess conse- 
quence in the case of prairie dogs, which are deep-burrowing animals, 
than in the case of pocket gophers and ground squirrels, whose bur- 
rows and tunnels, as a rule, lie much nearer the surface. 
Crude bisulphide, suitable for killing prairie dogs and other bur- 
rowing animals, costs about 10 cents per pound in 50-pound carboj^s 
or drums. A dollar's worth is enough to poison 100 holes. The cost, 
therefore, is about 1 cent a hole. The fluid should not be introduced 
haphazard into the burrows of a colony, but should be used only in 
those which the animals have been seen to enter immediately before it 
is applied. In this wa}^ none is Avasted on unoccupied holes. 
GENERAL DIRECTIONS FOR PRAIRIE-DOCi DESTRrCTION. 
Poisons are of very little use except in winter and earlv spring, 
when the ordinary food of the prairie dog is scarce and difficult to 
obtain. At such times poisoned grain, vegetables, fruit, and bread 
and butter are freely eaten. In distributing the poisoned grain or 
other material, it is usuallv better to scatter it about the holes instead 
of putting it into the mouths of the burrows, where it gets mixed 
with the dirt and is trodden down by the animals and lost. An excep- 
tion to this course is recommended in case of the use of pellets of grain, 
made b}^ wrapping teaspoonful doses of poisoned grain in greasy tissue 
paper; these should be dropped into the l)urrows. The danger to stock 
is much less when the grain is scattered about the colony than when 
it is placed in spoonfuls at or near the openings of the ))urrows. In 
case any considerable number of animals are left after the first poison- 
ing the ground should be gone over a second time. 
It should be clearly understood that the method recommended b}^ 
this Department consists in two steps, the first of which is to destroy 
the great bulk of the inhabitants of a colony by poisoning with 
str3X'hnine, applied in winter or earh^ spring when food is scarce; the 
second, to kill the remaining animals with bisulphide of carbon. In 
this way it is believed that colonies of an}^ size may be wiped out at a 
total cost not to exceed 16 or IT cents per acre, probablv less. 
Bisulphide is probably the most efficient single agent known for 
the destruction of prairie dogs, and can be used, of course, for the 
