The Stizus Sand Wasps

Some years ago, I presented a post on the sand wasps of the tribe Bembicini. Bembicini are just part of the broader range of sand wasps that have been variously classified as the Bembicidae, Bembicinae or Nyssoninae (Bohart & Menke 1976; Sann et al. 2018). Another diverse subgroup of the bembicids is the genus Stizus, of which more than 120 species are found in Eurasia, Africa and North America (but not in Australia or South America). Stizus species are relatively large wasps, getting up to 3.5 cm in length. Like Bembicini, they are often brightly coloured, black banded with yellow and/or red. They are otherwise fairly generalised in appearance: the labrum is exserted but is not remarkably long like that of bembicins, and the ocelli are not reduced (Bohart & Menke 1976).

Stizus pulcherrimus, copyright Phonon B.

The nesting behaviour of Stizus species was reviewed by Evans & O'Neill (2007). All known Stizus nests are constructed in soil and sand, sometimes in relatively damp locations such as salt marshes or near water bodies. Burrows of nests may be a foot or more deep and contain multiple cells; acessory burrows are common. Though females construct their burrows strictly single-handedly, they will often nest in clusters with other females. Polidori et al. (2008) found that this clustering behaviour in the European Stizus continuus was due to females being actively attracted to nests of other females, rather than just a side effect of limited nest sites. The most commonly used prey are various Orthoptera (grasshoppers or katydids); a handful of species instead prey on mantids. Prey are paralysed by repeated stinging before being flown back to the nest carried under the female. After the prey insect has been placed in a nest cell, the female lays an egg on its thorax. In most cases, cells are fully stocked with prey before laying, but females of S. continuus have been observed carrying fresh prey back to nests in which larvae have already hatched and begun eating.

Stizus perrisi female constructing nest, copyright David Genoud.

Mating between males and females generally occurs as the newly matured females emerge from the parent nest. Males often emerge before females and begin patrolling the nesting area, searching for females and chasing away other males. In some cases, they may begin actively digging for females emerging from burrows, and a newly emerged female may find herself surrounded by a pack of competing males. In their eagerness, males may become rather hasty: males of the Japanese S. pulcherrimus have been observed attempting to force themselves on females of the related genus Bembix!

REFERENCES

Bohart, R. M., & A. S. Menke. 1976. Sphecid Wasps of the World. University of California Press: Berkeley.

Evans, H. E., & K. M. O'Neill. 2007. The Sand Wasps: Natural History and Behavior. Harvard University Press.

Polidori, C., P. Mendiola, J. D. Asís, J. Tormos, J. Selfa & F. Andrietti. 2008. Female-female attraction influences nest establishment in the digger wasp Stizus continuus (Hymenoptera: Crabronidae). Animal Behaviour 75: 1651–1661.

Sann, M., O. Niehuis, R. S. Peters, C. Mayer, A. Kozlov, L. Podsiadlowski, S. Bank, K. Meusemann, B. Misof, C. Bleidorn & M. Ohl. 2018. Phylogenomic analysis of Apoidea sheds new light on the sister group of bees. BMC Evolutionary Biology 18: 71.