Kleptoparasitic behaviour of Aphodius rufipes (L.) larvae in nests of Geotrupes spiniger Marsh. (Coleoptera, Scarabaeidae)

1. Third instar larvae of A. rufipes were found in short vertical shafts in the soil beneath horse dung and they entered the underground brood masses of G. spiniger when these occurred beneath the same deposit of dung. 2. A.rufipes larvae excavated shafts (60-80 mm deep) beneath dung in cages. Just before diapause they burrowed down to the floor of the cage. Burrowing was inhibited in compact soil and in very dry soil. The feeding larvae were attracted to dung and to moisture and they readily attacked other larvae with their mandibles. 3. In cages which contained G. spiniger nests the A. rufipes larvae burrowed down to feed on the G. spiniger brood masses. G. spiniger eggs and larvae did not act as attractants but they were often destroyed if the A. rufipes larvae encountered them by chance. 4. In cages which contained G. stercorarxus nests A. fossor larvae burrowed down to feed on the brood masses if no dung was provided at the surface. 5. This non-obligatory parasitism arises from the normal behaviour of the larvae and is usually of trivial significance, but under certain conditions the protected environment of an underground nest may favour the survival of the invading larvae.