The Running of the Termites

I don't know how many people would profess to have a favourite genus of termites. Which is a shame, because there are some real stand-out examples. Snapping termites, magnetic termites, glue-spraying termites... For my own part, though, I have a particular fondness for the Australian harvester termites of the genus Drepanotermes.

Soldiers and workers of Drepanotermes perniger, copyright Jean Hort.

Nearly two dozen species of Drepanotermes are found on the Australian continent to which they are unique (Watson & Perry 1981). They are arid-environment specialists, being most diverse in the northern part of Australia. My reasons for being so fond of them are, I'll admit, decidedly prosaic. The worker caste of most termite species is very difficult if not impossible to identify taxonomically; one termite worker usually looks very much like another. Drepanotermes workers, however, are different. The name Drepanotermes can be translated as "running termite" and, as befits their name, Drepanotermes of all castes stand out for their distinctly long legs. Soldiers of Drepanotermes also have distinctively shaped mandibles which are sickle-shaped and have a single projecting tooth on the inner margin. They are similar to soldiers of the related genus Amitermes (of which Drepanotermes may represent a derived subclade) but the mandibles of Amitermes tend to be straighter and more robust.

The long legs of Drepanotermes reflect their active harvester lifestyles. Workers will emerge from the nest at night in search of food to carry back home. In the red centre of Australia they will primarily collect spinifex; they will also take fallen leaves, tree bark and the like. Soldiers keep guard while the workers forage. I've found them clustered around a nest entrance of an evening, just their heads poking out to snap at passers-by. Workers may wander up to about half a metre from the nest entrance as they forage. The concentrations of vegetable matter produced by Drepanotermes storing food sources in their nest may form a significant factor in the nutrient profile of areas where they are found.

Alate and soldiers of Drepanotermes rubriceps, copyright Jean Hort.

Depending on species and circumstance, the nests of Drepanotermes may be mounds or entirely subterranean with the latter being the majority option. They prefer compact soils such as clay though they may burrow through looser soils where there is a denser subsoil. Drepanotermes may construct their own nest or move into nests constructed by other termites. One aptly named species, D. invasor, seems to take over pre-existing nests more often than not. Subterranean nests are arranged as a series of chambers about five to ten centimetres in diameter connected by tunnels. These chambers may be arranged vertically, one below another, or they may form a rambling transverse network. Above ground, subterranean nests may be visible as an open circle devoid of vegetation. The ground in these circles is hard as concrete and may remain clear for decades after the actual nest has gone. Walsh et al. (2016) refer to the remains of nests protruding above ground along vehicle tracks after the soil around them has worn down. Local people have a long history of taking advantage of the open space offered by termite nests, such as to move more easily through scrub or as resting or working places.

The alate castes of Drepanotermes tend to be poorly known. Indications are that mature reproductives spend little time in the parent nest before leaving to breed. For most species, breeding flights take place in late summer. Alates may emerge either by day or night. The time of emergence seems to depend on the species; night-flying alates have distinctly larger eyes than day-fliers. Unfortunately, because alates have rarely been collected in association with a nest, we are largely still unable to tell which alates belong to which species.

REFERENCES

Walsh, F. J., A. D. Sparrow, P. Kendrick & J. Schofield. 2016. Fairy circles or ghosts of termitaria? Pavement termites as alternative causes of circular patterns in vegetation of desert Australia. Proceedings of the National Academy of Sciences of the USA 113 (37): E5365–E5367.

Watson, J. A. L., & D. H. Perry. 1981. The Australian harvester termites of the genus Drepanotermes (Isoptera: Termitinae). Australian Journal of Zoology, Supplementary Series 78: 1–153.