Based on sex-ratio analysis, thelytokous parthenogenesis is shown to be widespread in the mite taxon Desmonomata (Nothroidea sensu lato), with four of the seven families completely thelytokous and a fifth nearly so. Monthly samples from populations in central New York State, Japan, and Canada, representing 22 species in five families, indicate that sex-ratios are constantly highly femalebiased, with thelytoky probably being obligate. Similar sex-ratios regardless of provenance show that there is no geographic parthenogenesis phenomenon. Our data suggest that thelytoky is not an adaptation for particular environments, that this reproductive mode is not recent in these mites, and that speciation and evolutionary radiation probably occurred in the absence of biparental reproduction.