Williamsita

Williamsita cf. bivittata, copyright David Francis.

Belongs within: Crabronini.

The subgenus Androcrabro of the genus Williamsita is an Australasian group of wasps with a modified antenna in the male (Bohart & Menke 1976).

On Williamsita
Published 28 May 2022

A while back, I wrote a post about the crabronid wasp genus Podagritus. This time, I’m going to cover another crabronid genus found here in Australia: Williamsita.

Like Podagritus, Williamsita species are boldly coloured wasps, typically mostly black with contrasting yellow or orange markings. They differ from Podagritus species in being more robust with the base of the gaster not notably pedunculate. Other distinguishing features include the presence of distinct foveae (pits) against the margins of the eyes (occasionally less distinct in males), thirteen-segmented antennae in males, and a pygidial plate in both sexes that is narrowed and concave in females, quadrate in males. Williamsita species also do not have the palps reduced as in Podagritus, instead having the more typical arrangement of six segments in the maxillary palps and four segments in the labial palps (Bohart & Menke 1976).

To date, eleven species have been recognised in the genus Williamsita (Leclercq 2006). Most are found in Australia with a single species each known from New Caledonia and Vanuatu. Leclercq (1950) suggested dividing the genus between two subgenera with all species except the New Caledonian type species W. novocaledonica forming a subgenus Androcrabro. Features supporting the latter taxon included the presence of ventral notches on one or more segments of the antennae in males. However, Leclercq later suggested abandoning such a formal division, questioning its significance (Leclercq 2006). The Australian species of Williamsita are, nevertheless, distinct from the two insular species in being marked with much stronger punctation over the body.

Most Williamsita species remain little seen and poorly known. However, breeding habits have been recorded for two Australian species, W. bivittata and W. tasmanica (Maynard & Fearn 2021; McCorquodale et al. 1989). Both these species nest in branching holes in rotting wood, either commandeering burrows left by wood-boring insects or excavating their own. Prey consists of larger flies such as blow flies or soldier flies which were carried back to the nest by the wasp running with the fly carried below the body. Up to six paralysed flies might be placed lying on their backs in a nest cell with an egg laid across the ‘throat’ (i.e. at the joint between head and thorax) of one of the flies. The cell would then be closed with a plug of woody frass. McCorquodale et al. (1989) recorded W. bivittata constructing several such cells in a series along a single tunnel, whereas Maynard & Fearn (2021) found W. tasmanica more likely to place a single cell in a side-branch. As both observations were limited to a single location in a single season, though, one might reasonably question whether these represent true differences in species behaviour or were determined by available conditions. There’s a limit to how deep a Williamsita can burrow.

Systematics of Williamsita
<==Williamsita Pate 1947BM76 [incl. Androcrabro Leclercq 1950L06, C85]
|--*W. novocaledonica (Williams 1945) [=Crabro novocaledonicus]BM76
|--W. bivittata (Turner 1908) [=Crabro bivittatus, W. (Androcrabro) bivittata]C85
|--W. bushiella Leclercq 1974 [=W. (Androcrabro) bushiella]C85
|--W. manifestata (Turner 1915) [=Crabro (Solenius) manifestatus, W. (Androcrabro) manifestata]C85
|--W. neglecta (Smith 1868) [=Crabro neglectus, W. (*Androcrabro) neglecta]C85
|--W. ordinaria (Turner 1908) [=Crabro ordinarius, W. (Androcrabro) ordinaria]C85
|--W. riekiella Leclercq 1974 [=W. (Androcrabro) riekiella]C85
|--W. serena (Turner 1915) [=Crabro serenus, W. (Androcrabro) serena]BM76
|--W. smithiensis Leclercq 1954 (see below for synonymy)C85
|--W. tasmanica (Smith 1856) [=Crabro tasmanicus, W. (Androcrabro) tasmanica]C85
`--W. vedetta Leclercq 1974 [=W. (Androcrabro) vedetta]C85

Williamsita smithiensis Leclercq 1954 [=W. (Androcrabro) smithiensis, Crabro tridentatus Smith 1868 non Fabricius 1775, W. tridentata]C85

*Type species of generic name indicated

References

[BM76] Bohart, R. M., & A. S. Menke. 1976. Sphecid Wasps of the World. University of California Press: Berkeley.

[C85] Cardale, J. C. 1985. Vespoidea and Sphecoidea. In: Walton, D. W. (ed.) Zoological Catalogue of Australia vol. 2. Hymenoptera: Formicoidea, Vespoidea and Sphecoidea pp. 150–303. Australian Government Publishing Service: Canberra.

Leclercq, J. 1950. Sur les crabroniens orientaux et australiens rangés par R. E. Turner (1912–1915) dans le genre Crabro (subgenus Solenius). Bulletin et Annales de la Société Entomologique de Belgique 86 (7–8): 191–198.

[L06] Leclercq, J. 2006. Hyménoptères crabroniens d’Australie du genre Williamsita Pate, 1947 (Hymenoptera: Crabronidae). Notes Fauniques de Gembloux 59 (2): 115–119.

Maynard, D., & S. Fearn. 2021. Ecological and behavioural observations of a nesting aggregation of the endemic Tasmanian digger wasp Williamsita tasmanica (Smith, 1856) (Hymenoptera: Crabronidae: Crabroninae). Papers and Proceedings of the Royal Society of Tasmania 155 (1): 43–50.

McCorquodale, D. B., C. E. Thomson & V. Elder. 1989. Nest and prey of Williamsita bivittata (Turner) (Hymenoptera: Sphecidae: Crabroninae). Australian Entomological Magazine 16 (1): 5–8.

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