Williamsita

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.

Williamsita sp., copyright David Francis.

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.

REFERENCES

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

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.

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.

Podagritus in Australia

The digger wasps of the tribe Crabronini are a widespread group distinguished by a boxy head shape and relatively stout mesosoma. They are not dissimilar to hairless bees and indeed are close relatives of that group. There is a wide diversity of crabronins around the world; among their representatives here in Australia are members of the genus Podagritus.

Podagritus cf. tricolor, from Insects of Australia.

Podagritus species are medium-sized, elongate crabronins, generally in the region of a centimetre in length (give or take a few millimetres). The gaster is pedunculate (that is, the first segment of the metasoma is drawn into an elongate peduncle). Other, finer features distinguishing them from related genera of crabronins include a palpal formula of 5-3 (referring to the number of segments in the maxillary and labial palps, respectively; 5-3 indicates that both palps are slightly reduced from the ancestral count for crabronins) and often the presence of a sharp subvertical ridge, the omaulus, near the front of the mesopleuron (the median plate on the side of the mesosoma). If the omaulus is not present as such, there is still a distinct curve where it would have been so the planes of the mesopleuron on either side are more or less perpendicular. Females have a well defined triangular, flat pygidial plate and males often have one as well (Bohart & Menke 1976).

Thirty species of Podagritus were recognised from Australia by Leclercq (1998). Other species of the genus are known from New Zealand and South America. Historically, the Australian species have been treated as a distinct subgenus Echuca from Podagritus elsewhere, based on features such as a well defined, flat prepectus and a weakly sculpted metapleuron. Leclercq, however, questioned the value of this distinction, noting the existence of a couple of Australian species sharing notable features in common with species found elsewhere, and suggested abandoning subgenera until the genus could be revised as a whole.

The natural history of Podagritus species in Australia remains poorly known. One species found in the east of the continent, P. leptospermi, has been found nesting in a sloping gravel bank (Bohart & Menke 1976). Burrows were near vertical and close to a foot deep, and contained two or three cells placed at the ends of lateral galleries (one cell per gallery). Entrances were surrounded by flat mounds of sand six to ten centimetres wide and were not closed while the female was out hunting. Cells were stocked with flies (Tachinidae and Therevidae, so presumably reasonably large) that were initially stored at the bottom of the burrow before being placed in the cell head inwards and belly up, in lots of four to six. The egg was attached to a fly between the head and thorax, so when the larva hatched it would find itself already in place on a welcoming bed of food.

REFERENCES

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

Leclercq, J. 1998. Hyménoptères sphécides crabroniens d'Australie du genre Podagritus Spinola, 1851 (Hymenoptera, Sphecidae). Entomofauna 19 (18): 285–308.

Tachytes: Crickets Face Death from Above

A Tachytes species feeding, copyright Stephen Cresswell.

Most people who are not entomologists assume that 'ants', 'bees' and 'wasps' are all mutually exclusive groups of animals. But while bees and ants are distinct from each other, they are both really distinctive subgroups of wasps. It is not difficult to find guides on the interwebs purporting to tell you the differences between a bee and a 'wasp', but many of the points usually cited will not apply to all wasps (usually what is intended is the differences between a bee and a social wasp, which is the type of non-bee, non-ant wasp most likely to make itself known to humans). Some wasps can look very similar to bees indeed.

Diagram of Tachytes ocelli, from here.

Tachytes is a large, cosmopolitan genus of not-quite-bees, including more than 250 species found on all continents except Antarctica. Its members are robust and hairy, and one would have to look very closely to spot the features marking it as a non-bee (such as the point that its hairs, though numerous, are not branched in the manner of a true bee). Tachytes is classified in the Crabronidae, the family of wasps believed to be most closely related to true bees (other crabronids have been featured in earlier posts: here, here and here). Like other crabronids, adult Tachytes are pollinators, feeding on nectar from flowers. Tachytes species can be separated from most other crabronids by the shape of the ocelli. As well as the two large compound eyes with their multiple lenses on either side of the head, many insects have three small single-lens eyes, called the ocelli, on the top of the head (some insects have fewer or no ocelli). When all three ocelli are present, they are arranged in a triangle with one at the front and two at the rear. In Tachytes, the rear ocelli are present but deformed (I presume non-functional, though I don't actually know). They are reduced to a pair of scar-lines shaped roughly like a comma, or the upper part of a question mark without the dot.

Female Tachytes sinensis sinensis with katydid prey, from here.

Like many other wasps, female Tachytes dig burrows in which they they sequester other insects in a paralysed state to provide food for their young (the big change between bees and other wasps was the provision of their larvae with a plant-derived food source such as honey or pollen instead of animal matter). The size of the burrow varies from species to species, but some are quite extensive: the North American species T. praedator digs a burrow with a centimetre-wide entrance about a metre long, with a 70 cm down-shaft followed by a horizontal run of about a foot (Lin 1967). This species digs at night, thus presumably both avoiding the heat of the day and reducing the risk of detection by predators or parasites. The top of the burrow is usually marked by a heap comprised of the removed soil from its digging; in some species, the female will close over the top of the burrow when not actively digging. A series of cells are constructed branching from the end section of the burrow; each of these cells is filled with enough prey to feed one larva, then an egg is laid in the cell and its entrance sealed. Most Tachytes species feed their larvae with Orthoptera such as crickets, grasshoppers or katydids; the exact type preferred differs between species, though I get the impression of a general correlation between the size of the Tachytes species and the size of its preferred prey. At least two exceptional Tachytes species from central Asia (T. ambidens and T. bidens) are known to supply their larvae with small caterpillars rather than orthopterans. The prey is carried by the female held by her legs, with the antennae clasped by the mandibles. Hunting behaviour has been described for two species from North America, T. intermedius and T. mergus, that stock their nest with pygmy mole crickets (Tridactylidae). Females of these species walk along the ground tapping at it with their antennae. When one locates a cricket in its underground burrow, she quickly digs downwards in an attempt to grab the cricket by its head with her mandibles and haul it out. Even if the cricket hears her coming and attempts to flee from its burrow, it may not escape. The wasp moves so quickly that she is often able to grab the cricket in mid-air as it leaps for freedom. These two Tachytes species also differ from others in the genus in that the crickets are sequestered in the nest not fully paralysed: it has been noted that mole crickets recovered from their nests are still quite mobile and even able to jump.

REFERENCES

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

Lin, C. S. 1967. Nesting behavior of Tachytes (Tachyplena) praedator Fox, with a review of the biology of the genus (Hymenoptera: Sphecidae: Larrinae). American Midland Naturalist 77 (1): 241–245.

A Skinny Waist is Not That Important

Female Clitemnestra bipunctata carrying prey back to its nest. Copyright Bill Johnson.

It's time for another post on crabronid wasps! The hard-working individual in the photo above is Clitemnestra bipunctata, a species found in the United States of North America. This is the only species of this genus found north of Mexico; other species are found in South America and in Australasia (Australia, New Guinea and New Caledonia). Clitemnestra belongs to the Gorytini, a closely related tribe to the Bembicini featured in an earlier post, though C. bipunctata is smaller than the average bembicin. You can find a good description of the biology of C. bipunctata at Bug Eric's website.

When Bohart & Menke (1976) prepared their revision of the Sphecidae (which then included the current Crabronidae), they included Clitemnestra in the genus Ochleroptera. Ochleroptera was recognised as closely related to Clitemnestra, but the two genera were distinguished by the shape of the metasoma (the effective abdomen). In Ochleroptera, the first segment of the metasoma is relatively long and narrow, and there is a distinct constriction between it and the remainder of the metasoma (you can see this clearly in the picture above). In Clitemnestra, this segment is shorter and broader, and it is not so divided from the other segments. Because the latter arrangement is the more primitive, Bohart & Menke suggested that Ochleroptera was descended from Clitemnestra, and because both genera were found in both South America and Australasia, they suggested that the two genera had both originated in Australasia and dispersed independently to South America.

Habitus of Clitemnestra noumeae, from Ohl (2002).

However, it was soon realised that the distinction between the two genera was not as clear as had been thought. A number of species were identified in South America in which the segment shape was intermediate: a bit long and narrow for 'Clitemnestra', but not narrow enough for 'Ochleroptera'. As there were no other significant features distinguishing the genera, they were eventually synonymised. Subsequently, Ohl (2002) described another species, Clitemnestra noumeae, from New Caledonia that also has an intermediate metasomal form. Though no formal analysis has yet been done to confirm things one way or another, it seems likely that 'Clitemnestra' and 'Ochleroptera' do not represent independent dispersals between Australasia and the Americas. Instead, 'Ocheroptera' species have probably arisen independently within Clitemnestra on more than one occasion.

To date, Clitemnestra bipunctata is the best studied species in the genus natural history-wise; other species have only been described on sporadic occasions. Clitemnestra species nest in burrows in vertical banks, which they primarily stock with various species of leafhoppers. In the case of one Australian species, C. plomleyi, it was suggested that the burrows it was seen using were not dug by the wasp itself, but had been left behind by beetles or other wasps (Evans & O'Neill 2007). It remains to be seen whether this is typical behaviour for the species, or it may have represented opportunistic behaviour by one enterprising individual.

REFERENCES

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

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

Ohl, M. 2002. A new species of the wasp genus Clitemnestra Spinola, 1851 from New Caledonia (Hymenoptera, Apoidea, Crabronidae, Bembicinae). Deutsche Entomologische Zeitschrift 49 (2): 275-278.