Two nesting behaviours and life history of a subsocial African dung-rolling beetle, Scarabaeus catenatus (Coleoptera: Scarabaeidae)

Nesting behaviour of a large-sized dung beetle, Scarabaeus catenatus (Gerstaecker), was observed at the Tsavo West National Park, south-eastern Kenya. Although this species is taxonomically a member of a dung-roller group (that is, subfamily Scarabaeinae), it had not only a rolling behaviour but also a tunneller behaviour for nesting. In the former case, the scarab rolled a chunk or a ball of dung some distance (0.5-15.5 m) away from the dung pat and buried it under the ground. In the latter case, it dug a tunnel near the dung pat (0-1 m) and transported several pieces of dung into the burrow. In both cases, brood nests were completed by a female alone or by male-female co-operation. Four days after dung burial, the female made one to four brood balls out of buried dung, in each of which she deposited an egg. On the other hand, the male left the nest soon after the female completed oviposition. Even after oviposition, the female stayed in the nest and cared for her progeny until they emerged. This indicates that S. catenatus is subsocial. A major source of offspring mortality was likely to be predation by driver ants (Dorylus sp.). Most females seemed to breed one time in each of two or more successive rainy seasons.