Post-moult allogrooming

This will be the first of several posts featuring aspects of termite biology.

Like all arthropods, eastern subterranean termites (Reticulitermes flavipes) are covered with a rigid exoskeleton and need to moult in order to grow, a process also known as ecdysis. I won’t go into the details here, but here’s the short version: the old cuticle (that’s the tough, rigid part) separates from the epidermis (a layer of cells) underneath, the new cuticle forms under the old one on the epidermis, and moulting fluid fills the space in between. This fluid contains, among other things, enzymes that degrade the lower layers of the old cuticle. The fluid is then reabsorbed, and the insect breaks open the old cuticle and slowly, carefully pulls every part of its body out.

Newly-moulted termites, like the one in the video below, are soft, delicate, and very pale in colour, only darkening to their usual golden brown when the new cuticle hardens. Insects depend on their cuticle not just for protection against desiccation and physical trauma, but also against pathogenic microbes like fungi: they’re extremely vulnerable until it hardens.

The moult itself finished right before I started filming. It began with the termite lying on its back with its legs straight, all pointed toward the tip of the abdomen. Occasionally, peristaltic movements were visible, especially in the abdomen, and after some time, it became clear that it was slowly pulling its legs – and every other body part – out of its old, slightly translucent “skin”. I’m having a hard time finding the right words to describe what that looks like: I think I just need to get it on film. Nestmates came by from time to time and briefly investigated/groomed (typical behaviour), but they didn’t stay long, nor did they help.

As soon as the moulting termite broke open the old cuticle (= exuvia, at this point) and started to extricate itself, it was surrounded by nestmates, mostly workers, who set about grooming it thoroughly. The exuvia, which became bunched at the tip of the abdomen, was pulled off and eaten by at least two nestmates, This brings us back to the video: the exuvia is completely off at this point (a nestmate comes on screen at around the 45s mark holding a piece of it), and grooming continues in earnest.

The extensive post-moult grooming was, to me, the most interesting part of the video – and the reason I’m sharing it. Termites are social animals and keep each other clean through allogrooming (= grooming of others of the same species), a behaviour that has likely evolved in response to pathogen pressure in the nest environment. Their saliva is known to have antimicrobial properties, and grooming also lets them physically remove pathogenic spores from nestmates, preventing the spread of disease through the colony.

It’s normal to see occasional grooming in a healthy colony. A worker will get in the mood (anthropomorphism, but it’s the best way to describe it) and start grooming a nestmate. If that nestmate moves away and another is nearby, the worker will just switch targets and keep grooming. Periods of grooming are usually short – a bit here, a bit there – and I rarely see more than one termite grooming a single individual.

I can’t explain why they groom so much after a moult, but I can offer a few ideas: 1. If termites had a motto, it would be “waste not, want not”. They might be lapping up left-over moulting fluid or bits of cuticle; 2. Newly-moulted termites are vulnerable to injury and infection. It could be an effort to keep their nestmate clean/free of spores until the cuticle hardens; and/or 3. The goal may be to coat the new cuticle with saliva.

If anyone has anything to add, feel free to leave a comment below!

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