538 
Of all these natural enemies the weasel is probably the most de- 
structive. This little carnivore seems to have taken upon itself the 
regulation of overproduction among all the Rodentia. Skunks and 
foxes also make way with many of them. The larger owls kill many 
rats, and are probably responsible for killing more of them than any 
other animal except the weasel. The larger hawks also catch them 
occasionally, and are undoubtedly an important factor in checking 
any overabundance of rats in the fields. 
Although comparatively rare in the fields, the damage done 
within the county by rats in the immediate vicinity of man’s abode 
must amount to many thousand dollars each year. The heaviest 
loss is probably in granaries, elevators, and various other storehouses 
for grain or for flour or vegetables. They are very destructive to 
young poultry. Probably no small part of the loss of this kind com- 
monly attributed to weasels and skunks is due to rats. They are 
also great thieves of eggs. 
Of late, attention has been called to the fact that destruction of 
property by rats is the least important of their evil deeds. Far 
more serious is their agency in the spreading of infectious disease. 
The bubonic plague is spread entirely by means of the rat flea. Tri- 
chinosis among swine is perpetuated, so far as is known, entirely by 
rats. Trichine can only occur in hogs as a result of their eating the 
flesh of some infected animal, and the rat is the only other animal 
with which the hog comes in contact that is so infected. As they 
frequent in turn sewers, outhouses, granaries, storehouses, and 
pantries, they may also disseminate such diseases as typhoid, dys- 
entery, and tuberculosis. 
HOUSE-MOUSE. 
Mus musculus Linnezeus. 
(Syst. Naits ley mcSapeO2) 
The common house-mouse has followed the European races of 
man into all parts of the globe. So far back as the time of Kennicott’s 
papers on the mammals of Illinois (1856-1857) it had become fre- 
quent in the fields, digging burrows and laying up stores in them. 
It is very abundant in harvest fields in late summer and fall, often 
far outnumbering all the other species of small mammals taken to- 
gether. At that time traps set inside shocks of grain or corn will 
