Aggregate nesting is a selfish herd response to parasitic miltogrammine flies and nesting behaviors of Crabro cribrellifer (Hymenoptera: Sphecidae).

Abstract

The nesting behaviors of Crabro cribrellifer are described based on 149 individually marked females. At emergence there is a female biased sex ratio (1:3) and nest switching is not uncommon. Females are nesting in a 234 nest aggregation covering 2x65 m in area. Variability in three edaphic factors (soil temperature, hardness, and per cent moisture) has no influence on the distribution of nests within the aggregation. A significant positive correlation between wasp nest density and the number of parasitic miltogrammine flies present is shown. Yet, based on twenty excavated nests, the probability of cell parasitism decreases as nest density increases. This gives a selective advantage to those females nesting within aggregations and supports the ""selfish herd"" model developed by Hamilton (1971). The finding lends support to the semisocial pathway (Lin & Michener, 1972) for the evolution of insect sociality.