Specimens from epizootics of Sarcoptes scabiei in red foxes (Vulpes fulva) from New York, U.S.A., and red foxes (V, fulva), coyotes (Canis latrans), and wolves (Canis lupus) from Alberta, Canada were examined for variations in chaetotaxy and denticulation. A high frequency of setal anomalies (duplications, absences, and modified bases) was found on specimens from all hosts. It is suggested that the conditions associated with epizootics allow for increased phenotypic variability in this character and that the numerical fluctuations of populations during epizootics provide an opportunity for the genetic alteration of these mites. The central region of the dorsum is typically covered with large, well developed denticles. However, on some specimens a small area with only rudimentary denticles or sclerotized striae is present. On many specimens ventral denticles are lacking. The implications of these observations on denticulation are discussed in relation to the current systematics of the genus Sarcoptes.