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.

Two New Insect Orders?

When a new species of insect is described as being distinct enough to represent a new order, it's kind of a big deal. So it certainly caught my attention over the past year when, not one, but two species from Cretaceous Burmese amber were considered worthy of the honour. Now, I'm going to be up front here and say that, while both are very interesting specimens, in both cases I think that the 'new order' label may be a trifle overblown. What's interesting to me is that my reasons for thinking so are different for both. Let's take a look, shall we?

Lateral and dorsal views of holotype of Alienopterus brachyelytrus, from Bai et al. (2016). Pink scale bar = 1 mm.

The first was published in March of last year by Bai et al. (2016) under the name of Alienopterus brachyelytrus. In overall appearance, Alienopterus resembled a long-legged cockroach, but with the head clearly visible instead of hidden by the pronotum in the cockroach manner. The head would have been mobile and capable of being turned in the manner of a modern cockroach or mantis. The forewings were hardened and reduced to small pads covering only the base of the hind wings, which retained their full length. The femora of the front legs bore a pair of dense rows of setae on their underside, and Bai et al. suggested that Alienopterus may have used these setae to help it grab prey.

A phylogenetic analysis of Alienopterus placed it together with the modern cockroaches and mantids, specifically as the sister group to the latter. Because Alienopterus lacked the primary distinguishing features of a mantis (such as the spined raptorial forelegs), and because of its distinctive wing morphology, Bai et al. made it the type and only species of a new order, the Alienoptera. But there are a number of reasons why I find this designation problematic. It is generally agreed these days that cockroaches and mantids (and termites) together form a clade known as the Dictyoptera. Many people have an idea that cockroaches are one of the oldest living groups of insects, having supposedly been around for hundreds of millions of years. But modern cockroaches and mantids only diverged sometime during the Jurassic and Cretaceous; earlier members of the Dictyoptera were cockroach-like, certainly, but they were just as close to mantids as to cockroaches, and also had features very distinct from either. If we are to recognise a distinct 'order' for Alienopterus purely on phylogenetic grounds, then we would also have accept several separate 'orders' for each of the various lineages of stem-dictyopterans. And as distinctive as Alienopterus is morphologically, it is not the only (or even the most) unusual member of the Dictyoptera. This is, after all, the lineage that has given the termites with their wood-chomping biology and baroque caste system, beetle-like taxa with full-on elytra, and active leapers like the Jurassic Skok svaba or the modern Saltoblattella montistabularis.

There is a definite paradox at play here. On the one hand, the question of which lineages get designated 'orders' is completely arbitrary because there is no formal definition for an 'order' except that it is a taxon that is somehow more significant than a 'family' (itself a completely arbitrary level). From that perspective, there is no inherent reason why the Dictyoptera should not get divided between any number of orders. But on the other hand, the concept of 'order' has a certain cultural cachet. 'Orders' are kind of the base units of entomology: the first thing that any student of entomology is likely to do is learn to distinguish between the various insect orders. Labelling a particular taxon an 'order' is a statement of value; it says that that taxon is somehow fundamentally important in a way that other taxa are not. And while, again, Alienopterus is a very interesting animal in terms of what it can potentially tell us about cockroach-mantis relationships, it is hard to see how it can be called 'fundamental'. There have been extinct 'orders' recognised from the fossil record, such as the Palaeodictyoptera, but such taxa represent notable radiations. With only a single known species, referring to Bai et al.'s taxon as 'Alienoptera' tells us little more than calling it an unplaced species within the Dictyoptera.

Various views of Aethiocarenus burmanicus from Poinar & Brown (2016).

The other new 'order' made its appearance in December, when Poinar & Brown (2017) published Aethiocarenus burmanicus (if you're confused about the date, it reflects the difference between the online and print publication). This was a very odd little insect: a flattened and wingless yet long-legged animal with long antennae. The most distinctive feature of Aethiocarenus is its head, which is globular with great bulging eyes and placed on a narrow neck. Poinar & Brown suggest that it may have made its living hunting in confined spaces, such as crevices in bark or among epiphytes. Because of its highly distinctive appearance from any other known insect, Poinar & Brown placed it in its own new order, the Aethiocarenodea.

In this case, my issue with the establishment of a new 'order' is that it is essentially a statement of ignorance. As distinctive as Aethiocarenus is, there are many equally unusual-looking insects that are not placed in their own 'order'—particularly among wingless forms that can get up to all sorts of freakiness. The overall 'jizz' of Aethiocarenus, particularly the distinct cerci, suggest that its affinities probably lie somewhere within the Polyneoptera, the group of insects including such forms as cockroaches, grasshoppers and stoneflies. Within other polyneopteran orders, a novice entomologist would be hard-pressed to recognise a sandgroper as a grasshopper, or the Javan cave-dweller Arixenia esau as an earwig. Similarly, without a formal analysis it is difficult to exclude the possibility that Aethiocarenus represents a kooky member of some already recognised order. And again, with only one known species, recognition of an 'order' Aethiocarenodea tells us little more than recognition of an unplaced Aethiocarenus.

REFERENCES

Bai, M., R. G. Beutel, K.-D. Klass, W. Zhang, X. Yang & B. Wipfler. 2016. Alienoptera—a new insect order in the roach-mantodean twilight zone. Gondwana Research 39: 317–326.

Poinar, G., Jr & A. E. Brown. 2017. An exotic insect Aethiocarenus burmanicus gen. et sp. nov. (Aethiocarenodea ord. nov., Aethiocarenidae fam. nov.) from mid-Cretaceous Myanmar amber. Cretaceous Research 72: 100–104.

Ami-, Ami-termes

Soldier of Amitermes, copyright Alexander Yelich.

I've referred before to my enthusiasm for termites, those wonderfully weird sociable scions of the cockroach clan. For today's post, I'm looking at one of the larger and most widespread termite genera, Amitermes.

There are over 100 species of Amitermes found in tropical regions around the world, though they are most diverse in Africa and Australia. They are members of the so-called 'higher termites' of the Termitidae, those termites with a gut microbiota dominated by bacteria rather than protozoa. Soldiers of Amitermes have long sickle-shaped mandibles with a more-or-less well-developed tooth on each mandible; these mandibles are used to slash at perceived threats, the effect of this direct attack being presumably exacerbated by offensive chemicals that seep from the fontanelle, a pore on the front of the head capsule. Members of the genus are diverse in habits: some build sizable mounds above ground whereas others live in small colonies in underground tunnels. Some show a distinct preference for living in the nests of other termites, either moving into abandoned mounds after the original owners have perished or squatting in some overlooked corner of an active nest. Nests may be built directly around a food supply, or workers may go out to forage for food to bring home. In the latter case, the workers may construct a covered tunnel for themselves as they go; these trails may commonly be seen running along the ground in areas where such termites are abundant. Many Amitermes species feed on wood but they may also take other vegetable matter such as grass. A number of species feed on the dung of herbivorous mammals such as cattle or horses (Gay 1968), digesting parts of the consumed plant matter that the original feeder could not. One West African species, A. evuncifer, is a significant pest of crops, attacking root vegetables or the roots of young trees. Hill (1942) noted that mound-building Amitermes could present difficulties beyond just their feeding habits, explaining that "The frequent destruction of nest of [this genus] is perhaps the most important task of those employed in the maintenance of certain northern aircraft landing grounds, for the removal of the original nest almost invariably is followed the erection of another of a size and consistency that contributed a potentially dangerous obstacle to landing or rising aircraft".

Magnetic termite mounds, copyright David King.

Perhaps the most famous members of this genus are the 'magnetic termites' of northern Australia. These are three species that build mounds that, instead of being conical or globular like the mounds of other species, are long and narrow, almost blade-like. Even more strikingly, they are lined up almost exactly along a North-South axis, with at most a 10° deviation. Experimental alterations of such mounds indicate that the termites are indeed sensitive to the direction of magnetic fields though other factors such as local climatic conditions may also play a part. The shape of magnetic mounds is usually interpreted as an adaptation for temperature regulation: at the cooler ends of the day, the mound is receiving the full effects of the sun but during the hot midday only the thin upper edge is in the line of the light. However elegant an explanation this may seem, however, it overlooks the detail that a more standard globular mound is actually better for heat regulation overall. Round mounds have a much lower surface area-volume ratio and hence a lower rate of heat diffusion. Blade-shaped mounds may absorb heat quickly in the morning but they also lose heat quickly at night. An alternative explanation for the mounds' shape may lie in where magnetic mounds are found. It is worth noting that only one of the Amitermes species concerned, A. meridionalis, is an obligate constructor of blade-shaped mounds; the other two species, A. laurensis and A. vitiosus, may build either conical or blade mounds depending on local conditions. Magnetic mounds are constructed on flat flood plains, so the termites living inside them build up stores of grass to provide food when flood-waters prevent them from foraging outside the nest. By allowing better air flow within the nest than a conical mound, the blade-shaped mounds allow food stores to remain edible for longer, reducing the risk of them expiring before flood-waters recede (Korb 2011). Temperature regulation is still the best explanation for the regular orientation, of course, but is probably not the primary cause for the mound form overall.

Drepanotermes rubriceps soldiers around a nest entrance, copyright Lochman Transparencies.

Phylogenetic analysis of the termites by Inward et al. (2007) indicated that the genus Amitermes as currently recognised is probably not monophyletic, being paraphyletic to at least the Australian genus Drepanotermes. Members of this latter genus are grass-feeders, particularly on the hard Triodia (spinifex) grasses that dominate large parts of arid Australia (and which few animals without the super-charged termite digestive system can eat). In my experience, Drepanotermes are one of the few termite genera that can be reasonably easily recognised from the workers alone, which are noticeably longer in the legs than other termites. I've often seen Drepanotermes workers out foraging at night; the entrance to the underground nest (a simple hole) can usually be found nearby. The soldiers do not usually emerge from the nest, but a group of them will sit in the entrance hole with their heads poking out to provide defence. When collecting specimens, I've found that the challenge is to move fast enough to grab a soldier before it zips back into the tunnel, escaping your grasp.

REFERENCES

Gay, F. J. 1968. A contribution to the systematics of the genus Amitermes (Isoptera: Termitidae) in Australia. Australian Journal of Zoology 16: 405–457.

Inward, D. J. G., A. P. Vogler & P. Eggleton. 2007. A comprehensive phylogenetic analysis of termites (Isoptera) illuminates key aspects of their evolutionary biology. Molecular Phylogenetics and Evolution 44: 953–967.

Korb, J. 2011. Termite mound architecture, from function to construction. In: Bignell, D. E., et al. (eds) Biology of Termites: A Modern Synthesis pp. 349–373. Springer.