Snap! goes the Termite

The snapping termite Cavitermes tuberosus, from Wiki Termes.

For the subject of today's post, I drew the termite subfamily Termitinae. Termites are extraordinary animals: socially complex, ecologically vital, dietically remarkable. Personally, I'm rather found of these communal cockroaches.

Termites of the family Termitidae (commonly referred to as the 'higher termites') differ from other, 'lower' termites in the nature of their gut biota (without which they would not be able to digest their cellulose diets): instead of having flagellated protozoa in their gut, termitids carry symbiotic bacteria. This difference in symbionts is reflected by a difference in diet. Higher termites feed on more decayed wood or plant matter than lower termites; some higher termites feed directly on organic-rich soil that contains little or no plant material (Inward et al. 2007). Subfamilies within the Termitidae are also distinguished on the basis of their gut anatomy: members of the Termitinae have what is called a 'mixed segment' on the outer edge of their intestine (Lo & Eggleton 2011). In the mixed segment, instead of the division between the mesenteron (the middle section of the intestine) and the proctodaeum (the posterior section) being simple and straight across, the mesenteron wall extends backwards along one side of the gut only; it has been suggested that the mixed segment functions to pump alkaline fluids into the gut, maintaining appropriate pH and fluid levels for the symbiotic bacteria in the hindgut (Bignell et al. 1983).

Workers of Amitermes dentatus repairing a damaged nest, from here.

The Termitinae have also been distinguished on the basis of the morphology of their soldiers, with most genera having soldiers with elongate mandibles that have relatively few large teeth. These are used to bite and slash at threats to the colony. However, phylogenetic analyses have contradicted this distinction (Inward et al. 2007). The Termitinae are paraphyletic with regard to the Nasutitermitinae, who have developed a very different method of defense: the mandibles are reduced, and instead the front of the head is drawn out into an elongate 'nose'. At the end of the 'nose' is a glandular opening from which the soldiers squirt a sticky glue at their opponents. Also nested within the Termitinae are the Syntermitinae whose soldiers combine both methods of defense: they retain sickle-shaped mandibles that are used to pierce the cuticle of attackers while the protruded glandular opening is used to apply toxic secretions. Chemical defenses are also not unknown among more standard termitines: soldiers of Globitermes sulphureus were dubbed 'walking bombs' by E. O. Wilson due to their explosive (and often self-destructive) discharge of toxic chemicals from hypertrophied labial gland reservoirs in the abdomen. It should also be noted that a small number of termitines do not produce soldiers at all: they may live in association with other soldier-producing termites, like the Australian Invasitermes, or they may feed on low-nutrient soils (presumably making the maintenance of a soldier caste too nutritionally expensive), like the Indomalayan genera Protohamitermes and Orientotermes.

The mushroom-like mound of Cubitermes, a major soil-feeding genus in Africa, photographed by Marco Schmidt.

Another mode of defense that is found only among the termitines (though phylogenetic analysis indicates that it has evolved multiple times) is the production of soldiers with elongate snapping mandibles. In these termites, soldiers store kinetic energy through muscular deformation of the mandibles, allowing them to be suddenly closed with great force (Prestwich 1984). So great is the force involved, in fact, that it seems to be not uncommon for the jaws to become completely crossed over as has happened to the individual at the top of this post. Snapping termites generally live in subterranean colonies, and even after the soldier has been 'spent' on the discharge of its mandibles, its body acts as a physical barrier in the confined tunnel. In some snapping termites, the mandibles are strongly asymmetrical, so the force of the closure is channelled through the left mandible only with doubled force. Asymmetrical snappers of the genus Neocapritermes, in fact, are able to knock out fairly large ants with a single blow. The video below shows a soldier of Planicapritermes attacking an ant: Or you can see Neocapritermes in action in this video. Keep a close eye on the screen around the 20-second mark...

REFERENCES

Bignell, D. E., H. Oskarsson, J. M. Anderson & P. Ineson. 1983. Structure, microbial associations and function of the so-called "mixed segment" of the gut in two soil-feeding termites, Procubitermes aburiensis and Cubitermes severus (Termitidae, Termitinae). Journal of Zoology 201: 445-480.

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.

Lo, N., & P. Eggleton. 2011. Termite phylogenetics and co-cladogenesis with symbionts. In: Bignell, D. E., et al. (eds) Biology of Termites: a modern synthesis pp. 27-50. Springer.

Prestwich, G. D. 1984. Defense mechanisms of termites. Annual Review of Entomology 29: 201-232.