Each of two nests that had been recently occupied was placed in a Berlese funnel, and in this way the arthropod fauna of the nests was collected. The most common arthropods in the nests were mites (parasitic, predaceous, and free-living) and springtails. Sowbugs, centipedes, spiders, and fleas were also present. Of these arthropods, the laelaptid mites, one kind of tick, and one kind of flea have a direct relationship with the vole. These parasites are the same species which are found on the vole itself. The mites were _Eulaelaps stabularis_ (Koch) and _Atricholaelaps glasgowi_ (Ewing). One adult tick, _Ixodes sculptus_ Newman, was in one nest. The fleas, about a dozen in each nest, were _Ctenophthalmus pseudagyrtes_ Baker, the flea most frequently found on the prairie vole. EXTERNAL PARASITES The pelage of prairie voles, pine mice, deer mice, and shrews forms a habitat for many kinds of parasitic arthropods. The fleas, lice, and mites from the prairie vole were collected, counted, and identified. The ectoparasites from the other small mammals living in the same habitat as the prairie vole were also considered. Some ectoparasites begin to leave the host when it dies, and any counts of ectoparasites made from snap-trapped voles may fall short of the number which was on the animal when it was alive. The average number of fleas recorded from live voles exceeds that found on snap-trapped voles (see table 4). The numbers of lice and mites were estimated, but selected voles were examined to obtain absolute numbers of these kinds of ectoparasites. The fleas, lice, and mites were mounted on one inch by three inch glass slides; the ticks were preserved in 70 per cent alcohol. Dr. E. W. Baker identified the mites; Dr. R. A. Cooley and Dr. Glen M. Kohls, the ticks; Dr. G. W. Wharton, the chiggers; and Dr. Gordon F. Ferris, the lice. To each of these gentlemen I am grateful. The fleas were identified by myself. FLEAS (SIPHONAPTERA) The information on the average numbers of fleas on voles was obtained from live-trapped and some snap-trapped voles. Fleas were counted only on voles which were removed from the traps within twenty-four hours after the traps had been last examined. The average numbers of fleas found on prairie voles in this study are given in table 4. TABLE 4. _Average Numbers of Fleas on Prairie Voles_[C] Subadults Adults Live-trapped voles 1.9 (73) 3.4 (29) Snap-trapped voles 1.1 (26) 1.3 (27) [Footnote C: The fleas on the live-trapped voles are all _Ctenophthalmus pseudagyrtes_ Baker, and those on snap-trapped voles represent several species (see table 2). The numbers in parentheses are the numbers of voles examined.]