Egg sac guarding by the funnel-web spider coelotes terrestris: function and development.

A number of spider species present a pattern of maternal behaviour labelled 'egg sac guardingŕs which consist of remaining close to the egg sac throughout the incubation period. The present study aims at assessing the function of this behaviour and at casting some light on its control mechanisms in Coelotes terrestris, a species which, unlike those previously studied, is sedentary and presents extended care of the young. Field and laboratory experiments have shown that the mother had a determining role in the protection of her progency against predators,which may include certain conspecifics, and parasites (acaria and moulds). Confronting females at various stages of the reproductive cycle with non-guarded egg sacs provided a certain amount of information on the development of egg guarding. Sub-adults ignored the egg sac (neither cannibalism nor egg guarding). Cannibalism was only exhibited by inseminated females which had not yet oviposited. The onset of egg guarding seemed to be linked with oviposition. No external stimulations were necessary for its maintenance and no extinction was observed. This indicated that the mother-young interactions which took place after emergence did not interfere with the tendency to guard the egg sac.