Telostegus

Telostegus inermis, copyright Roman.

Belongs within: Pompilinae.

Sociable spider-hawks
Published 21 October 2013

The wasp in the photo above (taken by Henrik Gyurkovics) is Telostegus inermis, a member of the family Pompilidae. I’ve always known pompilids by the vernacular name of spider-hawks; other names I’ve heard include spider-hunters or tarantula hawks. They get these names because the females capture spiders that they paralyse with their sting. The helpless spider is then dragged into a burrow, where the spider-hawk lays an egg on it. When the egg hatches, the spider will become food for the developing larva.

Spider-hawks of the genus Telostegus are known from the greater part of the Old World. Normally, at this point, I would say something about their distinguishing characters, but I’m afraid that you’ve got me there. A morning spent trying to dig up descriptions has largely failed, with the necessary references being scattered and inaccessible to yours truly. Though spider-hawks are among the more visible of wasp families, they have not been that extensively studied. Indeed, one of the first things I came across in my search was this dis-heartening exchange discussing how there was (as of 2009) only one researcher in Europe with the experience to reliably identify pompilids, who is difficult to contact due to failing health. Sadly, this is a scenario all too familiar in the world of taxonomy.

The nesting behaviour of three Australian Telostegus species (one under the since-synonymised genus Elaphrosyron) was described by Evans & Matthews (1973). Each built nests in which a single entrance lead through branching tunnels to multiple cells, each containing a single spider. In at least one species, Telostegus socius, the soil from the burrow was piled in a mound in front of the entrance. Evans & Matthews also noted that another pompilid species, Ceropales ligea, would sometimes lay its own eggs on the Telostegus‘ spider as the female of the latter was in the process of transporting it, making C. ligea a cuckoo pompilid. The name of Telostegus socius refers to another characteristic of its nests: a large number of females would build their nests in close proximity. Such gregarious behaviour is also known from wasps in other families (such as the sand wasps of the crabronid genus Bembix). It does not represent true social behaviour like that of ants or vespid wasps, as each female is still constructing and stocking her own nest. Nevertheless, any would-be predators may now be faced with a whole group of defending wasps instead of just one, and it is tempting to see such gregarious nesting as an early step towards true social behaviour.

More on spider-hawks
Published 11 August 2015

A couple of years ago, I wrote the slightly abortive post above on wasps of the family Pompilidae, the spider-hawks. Despite their striking appearance and relatively high visibility, I noted, it was nigh on impossible to find reliable taxonomic information on them.

Diagram of the forewings of Cryptocheilus australis (above) vs Heterodontonyx bicolor (below) from Wahis (2008), showing the differences in the shape of the marginal cell (the large cell along the top margin of the wing).

This question came back to the fore for me recently when I had to attempt to identify a number of spider-hawks for work. With no recent key available for Australian pompilids, I had to try and piece together clues. As it turns out, a large part of the difficulty in identifying spider-hawks is that they are, overall, a conservative bunch. Though coming in a range of sizes and colours, they tend to be structurally uniform. This makes it difficult to find reliably key-able characters, and means that evolutionarily quite distinct species can look superficially quite similar. Take, for example, one of the most ‘familiar’ of the Australian pompilids, the black-and-orange Cryptocheilus bicolor. Recently, Wahis (2008) established that this was not a true species of Cryptocheilus, but belonged to a distinct (albeit related) genus as Heterodontonyx bicolor. The two genera can be distinguished by the shape of the marginal cell in the forewing, which is distally pointed in Heterodontonyx but rounded in Cryptocheilus. The thing is, many of the photos one may find online labelled as ‘Cryptocheilus bicolor‘ are true Cryptocheilus, not Heterodontonyx. Those on Wikipedia may be correctly identified, but these here are not. Not every large orange-and-black spider-hawk in Australia is Heterodontonyx bicolor.

Specimen of Telostegus inermis, copyright Josef Dvořák.

So what of Telostegus, the genus that I was complaining about being unable to find the diagnostic characters for in my earlier post? Evans (1972) describes it as having bifid tarsal claws, and a vena spuria in the forewing. A vena spuria (‘spurious vein’) is a fold in the wing that might be mistaken at first glance for a wing vein. In the images above, it can be seen as a dark line along the middle of the wing in the dorsal view. Evans (1972) separated two genera of spider-hawks, Telostegus and Elaphrosyron, on the basis of the number of submarginal cells in the forewing (two in Telostegus, three in Elaphrosyron) but more recent authors have not regarded this distinction as valid.

References

Evans, H. E. 1972. A review of the Australian species of Elaphrosyron and Telostegus, with notes on other genera (Hymenoptera: Pompilidae). Breviora 386: 1–18.

Evans, H. E., & R. W. Matthews. 1973. Behavioural observations on some Australian spider wasps (Hymenoptera: Pompilidae). Transactions of the Royal Entomological Society of London 125 (1): 45–55.

Wahis, R. 2008. Contribution à la connaissance des Pompilides d’Australie (Hymenoptera : Pompilidae). 2. Sur quelques spécimens récoltés par G. Else (Natural History Museum, London) avec descriptions de deux espèces nouvelles des genres Auplopus et Ctenostegus. Faunistic Entomology 61 (1–2): 23–31.

Systematics of Telostegus
Telostegus Costa 1887 [incl. Elaphrosyron Haupt 1929, Protelostegus Priesner 1955]E07
|--*T. major (Costa 1881) [=Aporus major]E07
|--*Protelostegus’ arnoldi Priesner 1955E07
|--T. cretensis Priesner 1965OY00
|--T. excisus (Haupt 1930)OY00
|--T. fumigatus (Klug 1834)OY00
|--*Elaphrosyron’ heinrichi Haupt 1930E07
|--T. imitator Priesner 1955OY00
|--T. inermis (Brullé 1832)OY00
| |--T. i. inermisOY00
| `--T. i. ater Haupt 1930OY00
|--T. nigrocinerascens (Turner 1910) [=Aporus nigrocinerascens]E07
|--‘Elaphrosyron’ paglianoi Wolf 1999OY00
|--T. socius (Evans 1972) [=Elaphrosyron socius]E07
|--T. thomisivorus Evans 1972E07
`--T. turneri Evans 1972E07

*Type species of generic name indicated

References

[E07] Elliott, M. G. 2007. Annotated catalogue of the Pompilidae (Hymenoptera) of Australia. Zootaxa 1428: 1–83.

[OY07] Özbek, H., E. Yıldırım, H. Wolf & R. Wahis. 2000. The Pompilidae (Hymenoptera: Aculeata) fauna of Turkey: part II. Pompilinae. Zoology in the Middle East 21: 109–128.

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