A B C D E F G ---------------------------------------------------------------- _Orchopeas leucopus_ (Baker) 0 0 53 31 37 6 10 _Orchopeas howardii_ (Baker) = _O. wickhami_ (Baker) 0 0 0 0 0 1 0 _Nosopsyllus fasciatus_ (Bosc) 0 0 0 0 0 1 0 _Epitedia wenmanni_ (Rothschild) 0 0 0 9 0 2 0 _Rectofrontia fraterna_ (Baker) 0 0 0 0 0 1 0 _Corrodopsylla hamiltoni_ (Traub) 47 8 0 0 0 0 0 _Ctenophthalmus pseudagyrtes_ Baker 0 38 0 0 4 25 53 _Peromyscopsylla scotti_ I. Fox 0 0 0 6 0 0 0 -------------------------- Total number examined 34 13 34 35 57 414 21 ---------------------------------------------------------------- [Footnote E: The numbers represent the percentage of each species which was parasitized by fleas. The mammals were collected at Lawrence, Douglas County, Kansas, between October, 1945, and June, 1946. These data are entirely from snap-trapped animals with the exception of those from _Microtus_ and _Pitymys_ which are from both snap-trapped and live-trapped animals.] It is seen that some fleas are rather specific in their choice of hosts, and that others are commonly found on two or more small mammals in the same habitat. In each of these groups there are fleas which have a habitat preference, that is to say, the flea lives on the host when the host lives in a given habitat, but is absent when the host lives in another habitat. GROUP 1: FLEAS WITH A HOST PREFERENCE _Epitedia wenmanni_ was found on the white-footed mouse (_Peromyscus leucopus_) and only rarely on the prairie vole. _Corrodopsylla hamiltoni_ was taken only from the two kinds of shrews (_Blarina brevicauda_ and _Cryptotis parva_). Fleas on shrews may have a well-developed host preference. At any rate, Elton, Baker, Ford, and Gardner (1931) found that _Doratopsylla dasycnemus_ rarely strayed from its normal host (_Sorex araneus_) to other small mammals. _Peromyscopsylla scotti_ was taken from the white-footed mouse (_Peromyscus leucopus_), and had a habitat preference also. It was found only on those white-footed mice which were trapped in the woodlands at various places in Douglas County; white-footed mice which were trapped in areas of brush were free of this parasite. GROUP 2: FLEAS COMMONLY FOUND ON TWO OR MORE KINDS OF SMALL MAMMALS _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.