A blog post highlighting the article written by Du, Chouvenc, Osbrink & Su in Insectes Sociaux

Written by Thomas Chouvenc

The queen is groomed by older workers. Notice how the cell around the queen is ‘clean’. Image credit: T. Chouvenc.

Well, they don’t exactly change diapers, but when it comes to the latrine and nest sanitation, old termites are in charge.

Age polyethism, where workers change tasks as they age, is an elegant way for social insect colonies to effectively allocate tasks to different individuals, usually giving the more risky duties, such as foraging out of the central nest, to older individuals. This process is mostly understood in honey bees and some ants. However, in termites, it’s a bit blurry.

There are about 3,000 described termite species, and they have historically been separated into two major groups: lower termites and higher termites. Lower termites are phylogenetically basal and possess protozoa for wood digestions, like their woodroach ancestors. Higher termites are more phylogenetically derived, and have radiated with a new type of symbiosis (fungal or bacterial) and have evolved unique derived morphologies, foraging strategies, and nesting habits.

When looking at polyethism in termites, most data from lower termites indicate that as workers age, there is little to no task division. In comparison, higher termites have documented cases of age polyethism, with older workers and soldiers foraging outside the nest. The genus Coptotermes is an interesting in-between case, as it is technically a lower termite because of the protozoa in the gut, but phylogenetically, and sometimes behaviorally, it is actually closer to higher termites. It is sometimes considered to be an evolutionary transition between lower and higher termites.

Du et al. (2016) investigated what is happening in nests of Coptotermes formosanus to determine if primary elements of age polyethism have evolved as an evolutionary step between lower and higher termites.

Juvenile colonies of C. formosanus (~1,500 individuals) were scrutinized using high-definitions cameras, and 34 hours of video recording were analyzed, documenting every single behavior that occurred throughout the nest. Du et al. identified 132 behaviors or types of interactions, for a total of 29,644 events, and the results showed that young workers and old workers performed different tasks, demonstrating primary elements of age polyethism.

The interactions between all individuals within the colony are rather complex, but some interesting patterns emerged from the observation:

• Old workers are more involved in foraging and trophallactic exchanges than the young ones, while young workers would predominantly groom larvae.
• Old workers are in charge of cleaning the royal cell and the maintenance of the queen.

The first observation was analyzed in detail, and the results showed that older workers are actually the primary individuals in the colony to be the recipient of proctodeal trophallaxis, i.e. feeding on somebody else’s poop. In a termite colony, the constant food sharing results in a social stomach, where the food is circulating among individuals, sharing the digestion process. However, at some point the proctodeal food reaches the point of being so poor nutritionally that it essentially becomes feces.

Invariably, older workers collected and ingested the feces, and ultimately, pooped it out somewhere in the nest. However, the fecal deposition was not random. Coptotermes termites create complex carton nests, which are the result of such fecal deposition. Therefore, instead of each individual pooping in the nest at their current location, all fecal matter is funneled through older workers, and ultimately reused as building material for the nest.

The second observation suggests that as older workers eventually travel to remote foraging sites, they can pick up the “queen signal” by grooming her and cleaning the royal cell, and then carry the signal throughout the nest, saying “the queen is alive.”

Editor’s note: This blog post is also published here.