Tillinae

Tillus elongatus, copyright Gilles San Martin.

The above individual is a representative of a species of the subfamily Tillinae of the beetle family Cleridae. Clerids are a widespread group of moderate-sized beetles, larger individuals being about a centimetre in length, but most species tend to attract little attention from humans. They are mostly predators in confined spaces (Gunter et al. 2013): larvae hunt down wood-boring insects in their burrows, or the young of bees and wasps in their nests, whereas adults hunt for other insects under bark. Adults are more or less elongate in shape and commonly have an even covering of setae and a prominently punctate dorsum. The legs have five-segmented tarsi, each tarsus often with multiple segments lobed. Clerids are commonly referred to as 'checkered beetles' in reference to the contrasting colour patterns of many species but, as you can clearly see, not all clerids have such checkered patterns.

The subfamilial classification of clerids has shifted around a lot in the past but the Tillinae have been one of the more consistently recognised subfamilies. The feature most consistently separating tillines from other clerids is that the fore coxal cavities are both externally and internally closed: that is, the external rim and internal collar around the fore coxae are both complete rather than being interrupted posteriorly. Other distinctive features of the tillines are that all five tarsal segments are well developed and distinct, the pronotum is campanulate (bell-shaped) or bisinuate, and the eyes usually have coarse ommatidia (Burke & Zolnerowich 2017).

Cylidrus megacephalus, copyright Udo Schmidt.

The taxonomy of tillines is (as always) in great need of study. Around 550 or more species have been assigned to the subfamily worldwide, with the highest diversity in the Afrotropical and Oriental regions. However, many species can be quite variable in appearance and it is suspected that many previously described species may turn out to be synonyms. The situation is not helped by many species being rarely collected. For instance, Bostrichoclerus bicornis is a remarkable species distinguished by the presence of a pair of prominent, apically bifurcate horns arising alongside the antennal insertions. To date, this species is known from just two specimens, collected at separate locations in Baja California and southern California (Burke & Zolnerowich 2017).

A molecular phylogenetic analysis of the Cleridae by Gunter et al. (2013) suggested that the Tillinae represent the sister group of all other clerids. While unexpected from a morphological perspective, this result does tally with the long recognition of the tillines as a distinctive group. They may prove to have interesting things to tell us about the evolution of the clerids as a whole.

REFERENCES

Burke, A., & G. Zolnerowich. 2017. A taxonomic revision of the subfamily Tillinae Leach sensu lato (Coleoptera, Cleridae) in the New World. ZooKeys 179: 75–157.

Gunter, N. L., J. M. Leavengood, J. S. Bartlett, E. G. Chapman & S. L. Cameron. 2013. A molecular phylogeny of the checkered beetles and a description of Epiclininae a new subfamily (Coleoptera: Cleroidea: Cleridae). Systematic Entomology 38 (3): 626–636.