An analysis of the nesting behaviour of Geotrupes spiniger Marsham (Coleoptera, Scarabaeidae)

1. Female G.spiniger adults working alone made nests each consisting of a vertical shaft leading to a series of horizontal brood chambers filled with dung brood masses. Oviposition near the tip of the brood mass occurred while the egg cell was being completed over the expanded ovipositor. The shaft above each brood mass was filled with soil excavated from the next brood chamber. A similar response also filled artificial diverticula. An avoidance reaction towards buried dung prevented damage to pre‐existing brood masses. 2. Virgin females did not make nests and did not avoid buried dung, but after mating (at about 4 weeks after eclosion) both types of behaviour were released within a few hours. 3. The presence of dung was required to initiate but not to maintain nesting behaviour. If dung was removed after oviposition the chamber was filled with soil produced by renewed excavation. Cellulose pulp could substitute for dung in brood mass formation. 4. Beetles interchanged between burrows at different stages before oviposition readily repeated all pre‐oviposition behaviour. They appeared to respond to the length of the shaft and of the brood chamber since they extended short shafts and short brood chambers considerably more than those of normal length. After oviposition the beetles continued to make brood masses even under abnormal conditions. 5. Tilting the cage through 90° caused beetles before oviposition to re‐orientate their burrowing direction, but tilting just after oviposition caused them to make vertical brood masses. Placing the shaft in a horizontal position towards the end of brood mass formation postponed the termination of this phase. 6. Beetles repeatedly excavated shafts and chambers when transferred to new cages. Conversely they repeatedly made brood masses when maintained in preformed plaster‐of‐Paris burrows. 7. This nesting behaviour can be described as a reaction chain in which each action generates its own terminating stimulus and initiates the subsequent response. The behaviour before oviposition could be omitted or repeated as required by the environment, but after oviposition there was little response to external interference. These characteristics have direct relevance to the survival of the larvae.