Larropsis

Larropsis uniformis, from Monarch.

Belongs within: Larrini.

Larropsis: letting your prey do the work for you
Published 12 June 2024

Keen-eyed wanderers in sandier regions of North America may observe wasps of the family Crabronidae going about their business, visiting flowers and hunting prey with which to stock their nests. Among the members of this family unique to this continent are species of the genus Larropsis.

Larropsis washoensis, from Monarch.

In their expansive review of the ‘sphecoid’ wasps of the world, Bohart & Menke (1976) recognised Larropsis as a genus of 25 species endemic to North America. Most of this species are found in the arid south-west of the United States, a couple inhabit the eastern seaboard, and none are found within the Mississippi basin. Most Larropsis species are black in coloration; a few have a red abdomen and the female of L. chilopsidis is almost entirely red. Representatives of Larropsis may be recognised by the reduction of the hind ocelli to elongate scars whose axes form an obtuse angle, and commonly by linear swellings on the frons along the inner margin of the eyes, with a small central tumescence above the antennal sockets. A sparse rake of spines is present on the fore tarsus of both sexes with only two spines on the second tarsal segment (species in other genera may have more). All these features are shared with the closely related genus Ancistromma which is more widespread across Eurasia and North America and is sometimes treated as a subgenus of Larropsis. However, the two were treated as distinct by Bohart & Menke (1976) owing to the presence in Larropsis of a horizontal carina on the side of the side of the mesosoma, below the insertion of the wings.

Larropsis interocularis, from Monarch.

The habits of Larropsis remain poorly known but where nests have been identified they are stocked with camel crickets of the family Rhaphidophoridae (Gwynne & Evans 1975). Those crickets that have been identified as targets of Larropsis are nocturnal species that dig themselves shallow burrows in sand for shelter during the day. The wasps enter these burrows and sting the slumbering cricket to paralyse it before laying an egg against the underside of the thorax, near the fore coxae. The wasp then digs around the entrance of the burrow to close it. Wasps may paralyse a cricket if they encounter it above ground but will seemingly abandon it if unable to transport it to a suitable burrow. Crickets recover from their paralysis over the following day, and regain the ability to move freely, but it is unclear if they are ever capable of escaping the closed-in nest before the wasp larva hatches.

The fact that Larropsis do not construct their own nesting burrow from scratch may explain the less developed tarsal rake than that of other genera. It also correlates with the development of the pygidial plate, which may bear a covering of appressed setae apically in contrast to the entirely shining plate of other genera. Bohart & Menke (1976) suggested that the ‘less developed’ characters of Larropsis were primitive for crabronids, but it is equally possible that they represent secondary adaptations to this genus’ mode of hunting. Gwynne & Evans (1975) observed that foraging Larropsis were often shadowed by satellite flies of the subfamily Miltogramminae, themselves would-be kleptoparasites of wasps such as Larropsis. Though the satellite flies closely followed foraging Larropsis, they would not enter cricket burrows themselves, and only oviposited on prey that was brought to the surface. Gwynne & Evans (1975) suggested that Larropsis’ mode of hunting might itself be a means of avoiding the depredations of miltogrammines. And besides, why go to the effort of digging yourself a nest when your prey is presenting you with one ready-made?

Systematics of Larropsis
Larropsis Patton 1892BM76
|--*L. tenuicornis (Smith 1856) [=Larrada tenuicornis]BM76
|--L. arizonensis Bohart & Bohart 1966BM76
|--L. atra Williams 1914BM76
|--L. chilopsidis (Cockerell & Fox 1897) (see below for synonymy)BM76
|--L. conferta (Fox 1893) (see below for synonymy)BM76
|--L. consimilis (Fox 1893) [=Ancistromma consimilis; incl. A. vegetoides Viereck 1906]BM76
|--L. deserta Bohart & Bohart 1966BM76
|--L. discreta (Fox 1893) [=Ancistromma discreta]BM76
|--L. divisa (Patton 1879) [=Larra divisa]BM76
|--L. elegans Bohart & Bohart 1966BM76
|--L. filicornis Rohwer 1911 [incl. L. yatesi Mickel 1918]BM76
|--L. greenei Rohwer 1917BM76
|--L. interocularis Bohart & Bohart 1966BM76
|--L. lucida Bohart & Bohart 1966BM76
|--L. rugosa (Fox 1893) [=Ancistromma rugosa]BM76
|--L. sericea Bohart & Bohart 1966BM76
|--L. snowi Bohart & Bohart 1966BM76
|--L. sonora Bohart & Bohart 1966BM76
|--L. sparsa Bohart & Bohart 1966BM76
|--L. striata Bohart & Bohart 1966BM76
|--L. testacea Bohart & Bohart 1966BM76
|--L. texensis Bohart & Bohart 1966BM76
|--L. uniformis Bohart & Bohart 1966BM76
|--L. vegeta (Fox 1893) [=Ancistromma vegeta]BM76
`--L. washoensis Bohart & Bohart 1966BM76

Larropsis chilopsidis (Cockerell & Fox 1897) [=Ancistromma chilopsidis; incl. A. tachysphecoides Viereck 1906, A. zerbeii Viereck 1906]BM76

Larropsis conferta (Fox 1893) [=Ancistromma conferta; incl. A. bruneri Smith 1906, Larropsis gracilis Rohwer 1915, L. minor Williams 1914, Ancistromma paenerugosa Viereck 1906]BM76

*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.

Gwynne, D. T., & H. E. Evans. 1975. Nesting behavior of Larropsis chilopsidis and L. vegeta (Hymenoptera: Sphecidae: Larrinae). Psyche 82 (3–4): 275–282.

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