i 5 6 



Insects and Disease 



stant use of the squirrel holes. The farmers in 

 some sections report that they frequently catch 

 more rats than squirrels in traps set in squirrel 

 holes at that season of the year. 



This close association of the rats and the squir- 

 rels affords a good opportunity for the fleas infest- 

 ing them to pass from one host to the other. 



So far only two species of fleas have been re- 

 corded from the ground-squirrels. One, Cerato- 

 phyllus acutus, is very common, sometimes literally 

 swarming over the squirrels, particularly if a squir- 

 rel is sick or weak from any cause. The other spe- 

 cies, Hoplopsyllus anomalus, is less abundant but 

 still quite common. Both of these species infest 

 rats also, so the chain of evidence is practically 

 complete. We have only to assume that at some- 

 time one or more of the plague-infected rats found 

 their way into the region where the squirrels were, 

 and the fleas passing from the rats to the squirrels 

 would carry the plague with them. 



The fact that the plague already has such a start 

 among the squirrels opens a new and very serious 

 phase of the problem of suppressing the disease. 

 All who have hunted the ground-squirrels will 

 testify to the readiness with which the fleas from 

 them will bite those who are handling them. As it 

 is the sick or weak squirrels that are most often 



