Paromalini

Predatory clowns
Published 10 August 2023

If you ask me (and really, why wouldn’t you?), a case can be made that histerids are among the most aesthetically pleasing of all beetles. The average histerid has a compact body form with elytra tightly fitted to the body and a sleek, shiny surface (the non-average histerid, in contrast, may be a twisted gorgon of baroque sculpting and long, glandular setae, but such figures are not the focus of our attention today). Elytral striae and/or punctures, if present, tend to form a curving pattern like tessellating arches. The vernacular name of ‘clown beetles’ has commonly been used for histerids though I have no idea why (I suspect it may be a laboured comment on their being ‘histerical’). Among these paragons of style are the various species of the tribe Paromalini.

Carcinops pumilio, copyright Udo Schmidt.

Characteristic features of the Paromalini include a short epistoma (the sclerotised lower region of the head between mandibles and frons) that is usually margined by the clypeo-frontal striae and, in males, an aedeagus with a long basal piece and relatively short parameres (Mazur 1993). Other features include a setose labrum, antennal cavities on the underside of the prothorax (into which the antennae can be retracted) that are not concealed by protrusions of the prosternum, outwardly arcuate sutures on the antennal club, a pair of apical spurs on the fore tibia, and mid and hind tibiae that are more slender than the fore tibiae (Kovarik & Caterino 2001). Mazur (1993) recognised twelve genera within the tribe.

Platyomalus aequalis, copyright Katja Schulz.

Like many other histerids, paromalins are predators on fly larvae. As such, they are typically associated with microhabitats where their prey may be found, such as accumulations of animal faeces. Carcinops pumilio is a globally distributed paromalin that has attracted attention as a potential controlling agent of house flies in chicken houses. Another group of Carcinops species found in deserts of North America includes species that are specialists in colonising patches of necrotic tissue on cacti (Reese & Swanson 2017). Damage to cacti causes the development of pockets of rot, that attract flies looking to lay their eggs on the decaying tissue, that attract histerids looking to feed on the flies. One nice little natural cycle, resulting in diversity amidst decay.

References

Kovarik, P. W., & M. S. Carerino. 2001. Histeridae Gyllenhal, 1808. In: Arnett, R. H., Jr & M. C. Thomas (eds) American Beetles vol. 1. Archostemata, Myxophaga, Adephaga, Polyphaga: Staphyliniformia pp. 212–227. CRC Press: Boca Raton.

Mazur, S. 1993. Notes on new and little known Oriental Histeridae (Col.). Revue Suisse de Zoologie 100 (1): 211–219.

Reese, E. M., & A. P. Swanson. 2017. A review of the cactophilic Carcinops Marseul (Coleoptera: Histeridae) of the Sonoran Desert region, with descriptions of six new species. Coleopterists Bulletin 71 (1): 159–190.

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