Abstract
In morphology, coloration, and size, Pseudabispa wasps (Hymenoptera: Vespidae: Eumeninae) closely resemble mason wasps in the genus Abispa, and their distributions overlap. Although these two genera are among the largest solitary wasps in Australia, the biology of Pseudabispa was not previously known. Field observations from near Katherine, Northern Territory, strongly suggest that P. paragioides (Meade-Waldo) females attack and kill female A. ephippium (Fabricius) and usurp their nests, then appropriate cells, mass provision them with caterpillars acquired by theft from still other nests, and close them with mud taken from the host nest. Despite an abundance of potentially available cells in nests of three other large solitary wasps common at the same site, P. paragioides was found associated only with nests of A. ephippium. This unusual report of apparently forcible and lethal interspecific nest takeover for a non-social wasp parallels behaviors previously known only from socially parasitic eusocial Hymenoptera. Exploitation by P. paragioides may help explain why its host displays some of the most highly developed parental care known in any solitary eumenid, and why its nests are spaced widely from one another.