Adult mites in the family Fedrizziidae are associated with passalid beetles, but their immature life stages have never been described. Herein, I describe the life cycles and illustrate the larva, protonymph and deutonymph of Fedrizzia grossipes Canestrini and Neofedrizzia camini Womersley . All life stages of both species fed on nematodes, and adults also scavenge upon dead mites, sometimes using their cheliceral excrescences to collect the internal juices from the carcasses. On a nematode diet at 25+/-1 deg. C, N. camini completed larva-adult development in 48+/-2 days and egg-adult development in 57+/-3 days; on the same diet, F. grossipes developed slowly, had high mortality, and rarely moulted into adults. Mating in N. camini occurred venter to venter, and post-copulatory mate guarding was observed, sometimes resulting in the death of newly-moulted females.