The following comments can be made concerning the specificity and geographic ranges of several species of mites: _Liponyssus occidentalis_ Ewing was found only on _Cryptotis parva_. _Eulaelaps stabularis_ (Koch) was one of the more common kinds found on the prairie vole. This mite is rather large (about 1 mm. long) and is frequently (with the following species) seen running through the pelage of its host. In addition to the records for this species in table 1, it was found to be a common parasite on _Pitymys pinetorum_ at Point Abino, Welland County, Ontario. Elton, Ford, Baker and Gardner (1931) found this same mite on _Apodemus sylvaticus_ and _Clethrionomys glareolus_ in England. _Atricholaelaps glasgowi_, like the preceding species, was one of the commoner mites on the prairie vole. It was found also on _Pitymys pinetorum_ at Point Abino, Welland County, Ontario; on _Microtus pennsylvanicus_ at Ithaca, Tompkins County, New York; and on _M. californicus_ at Calaveras Dam, Alameda County, California. _Atricholaelaps sigmodoni_ occurred only on the cotton rat. _Laelaps kochi_ was less commonly found than _Eulaelaps stabularis_ and _Atricholaelaps glasgowi_. In Kansas the prairie vole and the cotton rat were hosts to _Laelaps kochi_, and it occurred on _Microtus pennsylvanicus_ at Ithaca, New York, and on _M. californicus_ at Berkeley, California. Trombiculidae are commonly known by their larvae which are called chiggers or harvest mites. The white-footed mouse, the cotton rat, and the prairie vole were parasitized at Lawrence. In the winter these mites live in the ears of these small mammals, but in the summer they were found both in the ears and on the rump. Those obtained in winter were _Ascoschöngastia brevipes_ (Ewing); other species may be involved. Listrophoridae was represented on the prairie vole by a species of _Myocoptes_ and a species of _Listrophorus_. These mites cling to the hairs of their host, and do not occur on the skin of the voles. No evidence was seen that mites had any ill effect on the health of their hosts. No voles had scabs on the skin; and the ears were not swollen and disfigured as they sometimes are by chiggers. Although the identity of a specimen of mite could not be determined until it was mounted, a person could tell whether or not it was one of the larger, very active Laelaptidae, one of the hair-clinging Listrophoridae, or one of the tiny, orange Trombiculidae. On July 12, 1946, three prairie voles were examined to determine the number of mites they supported. The voles were freshly caught, no one of them having been dead for more than five minutes before they were examined. These three voles had an average of 25 Laelaptidae, 22 Listrophoridae, and 53 Trombiculidae.