Within single infestations the mean pre-molt period for engorged larvae of Aponomma hydrosauri at 25°C varied from 15 to 24 days, and for engorged nymphs from 20 to 33 days. The period decreased with increasing temperature but was not influenced by engorgement time or engorgement weight. Nymphs turning to females took longer than those turning to males. Differences were detected in the mean pre-molt periods from infestations on different individual hosts of the same species, from infestations on different host species, and from infestations of stocks from different localities within South Australia.