Thorictosoma sp., from Matthews & Bouchard (2008).

Belongs within: Tenebrionidae.

Dig, darkling
Published 17 April 2024

In a recent discussion about the general habitus of beetle families, I noted that tenebrionids may be recognised as the family whose members look like anything but tenebrionids. Some look like carabids, some like bostrichids, some even make a decent stab at looking like cerambycids. And then there are the Cnemeplatiini, the tenebrionids that look like scarabaeids.

Philhammus ferenczi, copyright Udo Schmidt.

Cnemeplatiins are small beetles, about two or three millimetres in length, with a moderately convex habitus. They have short antennae ending in a three-segmented club, and a strongly emarginate clypeus. They also have the tibiae of the front legs expanded and flattened, giving them an overall appearance remarkably similar to the small dung beetles of the Aphodiinae. These broad front legs are used to dig through the dry, sandy soil in which cnemeplatiins typically live. This habitat may also explain their lack of a sclerotised ovipositor, with females instead just dropping eggs behind them as they dig (Watt 1992).

Actizeta albata, copyright Saryu Mae.

Currently, species of Cnemeplatiini are assigned to nine genera divided between five subtribes (Aalbu et al. 2018). Only one of these subtribes, the Cnemeplatiina, is widespread globally (being found in Eurasia, Africa and the Americas); the remainder each contain only one or two genera unique to particular regions. The New Zealand Actizeta is an inhabitant of coastal sand dunes, feeding on plant debris. The Australian Thorictosoma exhibits reduced eyes and a large mentum covering most of the mouthparts (Watt 1992), perhaps reflecting an association with particularly dusty soil. Members of the remaining two subtribes are found in ant nests, with Alaudes found in southwestern North America and the two genera of Rondoniellina found in Southeast Asia. The exact nature of their association with their ant hosts remains poorly known. One species of Rondoniellina, Durandius ardoini, possesses reduced mouthparts and may be fed by its host via trophallaxis. But how it goes about it, and how it convinces the ants to play along, remains a mystery.

Systematics of Cnemeplatiini
| i. s.: ActizetaMB08
| Alaudes Horn 1870AT02
| Lepidocnemeplatia Kaszab 1938AT02
| `--L. sericea (Horn 1870)AT02
|--Wattiana Matthews & Lawrence 2005MB08
| `--*W. greensladei Mattthews & Lawrence 2005MB08
`--Thorictosoma Lea 1919MB08
|--*T. ectatommae Lea 1919MB08
`--T. tibiale Lea 1919MB08

*Type species of generic name indicated


Aalbu, R. L., M. S. Caterino & A. D. Smith. 2018. Studies in the Cnemeplatiini I: a new subtribe and revision of the genus Alaudes Horn (Coleoptera: Tenebrionidae: Pimeliinae: Cnemeplatiini), with descriptions of new species from the southwestern USA and Mexico, including notes on distribution and biology. Coleopterists Bulletin 72 (2): 249–268.

[AT02] Aalbu, R. L., C. A. Triplehorn, J. M. Campbell, K. W. Brown, R. E. Somerby & D. B. Thomas. 2002. Tenebrionidae Latreille 1802. In: Arnett, R. H., Jr, M. C. Thomas, P. E. Skelley & J. H. Frank (eds) American Beetles vol. 2. Polyphaga: Scarabaeoidea through Curculionoidea pp. 463–509. CRC Press.

[MB08] Matthews, E. G., & P. Bouchard. 2008. Tenebrionid Beetles of Australia: Descriptions of tribes, keys to genera, catalogue of species. Australian Biological Resources Study: Canberra.

Watt, J. C. 1992. Relationships of Actizeta and Cnemeplatiini (Coleoptera: Tenebrionidae). Systematic Entomology 17: 287–299.

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