Insect Bites: The Sunday Digest – Cheating the super-organism

A familiar sight for many people, whether they are entomologically inclined or not, is ants working in what appears to be a cohesive manner. Naturalists in the early twentieth century described these assemblies of individual ants as ‘super-organisms’.

Like bees, wasps and termites, ants are eusocial. This means within one species there are often workers, soldiers and queens. Each of these so called castes has its own unique role within the colony and appear very different to each other despite being the same species. Individuals in these complex societies would be unable to survive alone; colony life is essential for individual survival.

Despite ants being evolutionarily and behaviourally advanced when compared to many other organisms, one group of beetles have managed to exploit them in an incredible way.  This group of beetles are a sub-family of rove beetles called Pselaphinae, pronounced “Seh-LAH-Fin-Ee”. This sub-family contains around 10,000 described species with many still undiscovered in ecosystems all over the world, and many left in museum collections still un-named. They have evolved complex morphological (structural) features which mean they can co-exist with ants, utilise colony resources and benefit from the ants’ protection.

Within Pselaphinae, a group of 369 species collectively known as the Clavigeritae (“Cla-Ve-JEH-Ri-Tee”) have taken the cheating to a whole new level. They have managed to fool ants into trophallaxis, a phenomenon where the ants directly feed the beetles, mouth-to-mouth. This kind of behaviour makes it clear that Pselaphinae seem to be treated as just another ant in the colony, evading the usual aggressive behaviour that ants exhibit towards outsiders! To facilitate this mouth-to-mouth feeding, the Clavigeritae have evolved brush like features (Trichomes) on the base of the abdomen which exude a substance that the worker ants find attractive to feed on, and seems to calm any aggressive behaviour. In addition, the beetles’ mandibles are not designed for hunting or grabbing prey, but perfectly suited to direct feeding from ants, being non-serrated and often circular in shape.

The development of these close and complex relationships between ants and Pselaphinae must surely be the result of million years of co-evolution. With ants containing a similar number of species to Pselaphinae, this may go some way in explaining the incredible diversity of these ant-exploiting beetles as they have specialised and speciated (the formation of new species) in close accordance with ant diversification.

A recent paper, published in “Current Biology” by Joseph Parker and David Grimaldi, has shed light on when these advanced ant-loving beetles first evolved and backs up the idea that Pselaphinae and ants have co-evolved for tens of millions of years. A single ant-loving beetle found in Indian Cambay amber that is about 52 million years old shows that these ant-loving beetles were present before ants diversified and gained dominance in ecosystems.

The association between ants and the organisms that ‘love’ them is known as myrmecophily. Other than numerous myrmecophilous species of Pselaphinae, these interactions are also found in another sub-family of rove beetles, Aleocharinae. This sub-family is even more diverse than Pselaphinae, containing 13,000 or so described species. Some myrmecophilous species of Aleocharinae resemble ants with constricted waists and a tendency to walk among the long winding trails of ant workers where they blend in perfectly. They themselves do not produce a chemical that appeases the ants, as in Pselaphinae, but instead they groom and obtain odours directly from them, thus enabling them to co-exist with the ants and perhaps, more importantly, avoid predators.

The Aleocharinae species Thyreoxenus brevitibialis has integrated into termite colonies by evolving a body form extremely similar to that of termites. The most obvious feature this beetle has evolved is the swelling of the abdomen, also known as physogastry, a typical characteristic seen in its victim.

The clown and king of termitophily is without a doubt Coatonachthodes ovambolandicus. Physogastry (swelling of the abdomen) in this species enables it to mimic its host termites down to a tee. The illustration below does the talking, showing all legs and antennae replicated in the beetles abdomen.

 

Capture

Coatonachthodes ovambolandicus: the termite mimic. Side on illustration (left) and dorsal view (right). Dorsal view showing the physogastric abdomen from above with all appendages including antennae mimicking a termite worker. Illustration from Kistner (1968), adapted by Kleisner & Markoš (2005).

It seems social insects are a victim of their own success, and not by coincidence. It is said that ant biomass is similar to that of humans and their impact on the environment is significant due to hoarding of materials for nests. The same can be said of termites and their mounds. These resource rich locations are clearly attractive to other organisms. In particular, Pselaphinae and Aleocharinae rove beetles have managed to exploit these advanced social insects perfectly, evolving to cheat the super-organism.

 

Author – Joshua Jenkins Shaw (@jenksshaw)

Further reading

Kistner, D.H. 1968. Revision of the African species of the termitophilous tribe Corotocini (Coeloptera: Stapylinidae). I. A new genus and species from Ovamboland and its zoogeographic significance. Journal of the New York Entomological Society 76. P213–221.

Kleisner, K. & Markoš, A. 2005. Semetic rings: towards the new concept of mimetic resemblances. Theory in Biosciences 123. P203-222.

Parker, J. & Grimaldi, D.A. 2014. Specialized myrmecophily at the ecological dawn of modern ants. Current Biology 24. P1-7.

Wheeler, W.M. 1911. The ant colony as an organism. Journal of Morphology 22. P307-325.