The mite Kennethiella trisetosa is phoretic on adults of the wasp Ancistrocerus antilope and develops in the nest with immature wasps. Female mites and a large type of male develop oviparously, whereas a small male develops ovoviviparously. Small males kill each other, but are ignored by large males. But mating with females before small males are mature, large males may monopolize fertilization. Larvae of female wasps usually detroy mites within their cells but, as adults, are reinfested when mated by mite-bearing males. Each time a male wasp mates, about half of its mites transfer to the female. The population structure of the mites has resulted in female-biased sex ratios. Despite feeding by mites on wasp body fluids, the two species could be mutually beneficial.