Abstract
In many spider species, spiderlings spend several days aggregated in a mass immediately after emerging from the egg sac. During this period, which is called the gregarious phase, spiderlings do not eat. In this study, we conducted two experiments to clarify the benefits of the gregarious phase in a wolf spider, Pardosa pseudoannulata Boes. et Str. In one experiment, we examined the effect of the fasting period on spiderling development (duration until molting to the next instar and increment of carapace width). The fasting period was set at 1 d in one treatment and at 5 d in another treatment. In a second experiment, we examined the effect of aggregation on spiderling development. In one treatment, spiderlings were individually reared from the next day of emerging from the egg sac. In another treatment, spiderlings were allowed to aggregate for 5 d before being reared individually. In both treatments, the fasting period was set at 5 d. Spiderlings that fasted for 5 d molted after a significantly shorter feeding period than those that fasted for 1 d, although we observed no effects of aggregation. The feeding period corresponds to the post-gregarious period when females no longer guard their spiderlings. Our results suggest that the gregarious phase functions to shorten the post-gregarious period during which the spiderlings are exposed to natural enemies.
