Nest-site selection in the great golden digger wasp, Sphex ichneumoneus L. (Sphecidae)

Abstract. 1. Sphex ichneumoneus are solitary, ground-nesting wasps with apparently broad nesting requirements.
2. Nest-site selecting behaviour involves four levels of decisions. First, the wasps are not active unless temperatures are high and they are less active during cloudy weather. Second, at the beginning of a nesting sequence they generally fly to the site from which they emerged, but occasionally they fly to other flat, vegetation-free areas. Third, after landing, they engage in a predigging search of the area, walking around, looking into and briefly digging in the nests of other wasps. In this way they apparently compare and choose to begin digging in the warmest areas available which are not too close to other nests. Fourth, if the soil is too soft and collapses or if it is too hard-packed, the wasp resumes the predigging search. The preference for digging within a range of compactness means that they generally choose sandy loam.
3. Theory would suggest that the wasps may spend an optimal amount of time in the predigging search behaviour and that frequency-dependent selection may be an important factor in the choice of nesting sites.
4. By choosing nesting sites according to these rules, the wasps are ensuring that their offspring develop in the warmest and best-drained soils available.