_Orchopeas leucopus_ was an outstanding example of this group. It was
the most common flea on the deer mouse, the white-footed mouse, and the
cotton rat. In certain areas it was common on the two voles (_Pitymys
nemoralis_ and _Microtus ochrogaster_). _Ctenophthalmus pseudagyrtes_ is
the most abundant flea on the two kinds of voles and on the large shrew
(_Blarina brevicauda_), and was found sparingly on the cotton rat.
Several kinds of fleas do not belong in either of the above groups. Some
fleas were accidental strays from mammals not included in table 6; and
one flea (_Rectofrontia fraterna_) may prove to be a common nest
parasite. _Orchopeas howardii_ is common on tree squirrels (_Sciurus
niger_ and _S. carolinensis_). _Nosopsyllus fasciatus_ is a cosmopolitan
flea on _Rattus norvegicus_. _Rectofrontia fraterna_ was taken once from
a prairie vole. Since the only specimens in the University of Kansas
Entomological Collections are from "mouse nests," this flea may be found
to be a nest inhabiting parasite.
Some fleas are possible bridges by which a blood parasite could be
transmitted from one kind of a mammal to another. If _Ctenophthalmus
pseudagyrtes_ acted as the intermediate host of a disease-causing
organism, an epizootic from _Microtus ochrogaster_ might be transmitted
to _Pitymys nemoralis_ or to _Sigmodon hispidus_ or _Blarina
brevicauda_. There are several other such potential bridges for blood
parasites. Although table 6 does not prove that individual fleas wander
from one host to another, the frequency with which the several kinds of
fleas are removed from live mice suggests that the fleas occasionally do
so.