This study explores the relationship between staphylinid beetles of the genus Amblyopinus and their small mammal hosts. Previous studies had concluded that these beetles were parasitic and fed directly on blood, skin exudates, or other epidermal derivatives of their hosts. We examined the mode of attachment, behaviour, and feeding activities of 254 Amblyopinus (A. tiptoni and A. emarginatus) on 69 hosts which were captured in Sherman live traps. In addition, similar information and diurnal activity patterns were monitored for 11 beetles kept on two hosts (Peromyscus nudipes) over a period of 14 days. Beetles were found to be attached to the host only by grasping clumps of fur in their mandibles. No sign of damage to the skin of the host could be found. Feeding by the beetles on parasitic arthropods was observed and concluded to be the primary feeding habit. Beetles showed a strong circadian activity pattern, in which they are attached to the host during night-time hours and actively hunt in the nest during daylight hours. Attachment to the host is hypothesized to be primarily a vehicle for tracking prey of the beetles within the variety of nests used by any individual host. We conclude that these beetles are not parasitic but, instead, highly specialized predators on ectoparasitic arthropods, with specialized behavioural and morphological adaptations for their unique life style.