The latest research from the University of Florida looks at the behaviour termites exhibit when subjected to starvation.
For millions of years, termites have enjoyed being one of the few plant-feeding animals with the ability to access the dry, carbon- loaded matter stored in tree trunks. Yet although the termite diet is carbon-rich, it is notably nitrogen-poor. Termites acquire nitrogen via feeding, potentially with the help of symbiotic bacteria. With nitrogen being so valued within the colony, termites have developed a method to conserve it at all costs: cannibalism. It is widely accepted that all termite species cannibalise their sick, dying, and dead individuals. But what has not been studied on a large scale, until now, is the effect starvation – the removal of wood (cellulose) sources – has on this behaviour.
Previous research has indicated that cannibalism can play an essential role in helping a group of termites survive a period of starvation. But what strategy do subterranean termites employ, exactly? In a study published online in October 2019 in Insectes Sociaux,1 Thomas Chouvenc, Assistant Professor in Urban Entomology at the University of Florida, explored this in detail.
Cannibalism is an essential part of the cycle of nutrients within the colony as it allows precious resources to be reused by the society. When a termite consumes the carcass of its dead or dying nestmate, it recycles many important nutrients, including nitrogen. This behaviour also has the secondary benefit of sanitising the colony and reducing the risk of diseases within the social group (Chouvenc et al., 2009). In fact, termites will not leave a dead nestmate lying around for long – it is usually cannibalised by nestmates very rapidly.
It has been assumed that during times of starvation, soldiers would be eaten by nestmates first, as soldiers are nutritionally dependent on workers. Cannibalism would alleviate their burden on the society and recycle very precious resources toward the rest of the group. Also, it is thought that the termite group would suppress the production of new soldiers so that only workers would remain, in the hope of ‘rebooting’ the colony and reducing the feeding pressure even further (Su and Lafage, 1986). This strategy would lead to prolonged survival of the colony.
Chouvenc revisited this concept in his 2019 study by taking a much wider, whole-colony approach. Whereas previous researchers had subjected a small group of field-collected foraging termites to starvation, Chouvenc subjected ten entire young Coptotermes gestroi colonies to starvation. The idea was to investigate the theory on a wider scale, looking at colonies comprising around 3,000 termites, a healthy brood, overlapping generations of workers and soldiers, and the king and queen. The effects of starvation on larger termite groups, the brood, or the primary reproductives had never before been investigated.
The results of the study were surprising. As the termites began running out of food, nutritionally stressed individuals started accumulating in the colony. For termite larvae and workers, the lack of nutrition meant they failed to moult successfully, leading to their death and subsequent cannibalisation by nestmates. Therefore, the brood and young workers were the first ones to be eaten – not as survival rations for the group, but because they were the first ones to die during their moulting process, due to their state of starvation.
Next, termite soldiers started showing signs of slowdown as they are fed second-hand from workers. The remaining workers had to maintain their own metabolism and had nothing left to share with the soldiers, resulting in moribund soldiers, and subsequent cannibalism.
It is worth noting that the starving colony does not suppress the production of new soldiers, as previous research suggested. It is simply that starving presoldiers failed to moult into functional soldiers, and therefore died and were eaten, resulting in a lack of soldier replacement.
Finally, towards the end of the study, a handful of workers remained, with the king and queen being the last ones to die.
The research shows that rather than taking a proactive approach to conserve energy within the colony (by cannibalising soldiers, the most expendable caste and the biggest drain on resources), the termites’ survival strategy during starvation appeared to be simply to keep the king and queen alive for as long as possible. The royal termites were the last remaining, with all energy resources eventually funnelled to them. The cannibalism that occurred was not due to a strategic play on the part of the higher castes; it was merely a result of the weakest members of the colony expiring first and subsequently being consumed (for nitrogen conservation) by the other termites. It appears that no other cannibalism strategy kicks into gear when a colony is nutritionally deprived.
Worthy of note is that within the study, the old workers consumed many dead nestmates, which caused high levels of uric acid to build up in their bodies. This observation is typical of termite colony collapse, as there is a sudden excess of nitrogen available, something termite metabolism never evolved to cope with. Twenty days after the starvation was in effect, the colony started shutting down, and cannibalism was no longer observed. Dead bodies began accumulating in the colony and were not taken care of by the surviving workers, which were focusing only on the king and queen. In the end, the king and queen eventually starved to death too.
In a blog post discussing the study,2 Thomas Chouvenc summarised the findings: “Termites are fine-tuned to conserve nitrogen, because it’s always a primary limiting factor on colony growth. However, termites are terrible in their survival strategy during starvation events because, in fact, they don’t really have a strategy. Cannibalism kicks in to recycle nitrogen, but has little effect on survival itself. Unlike honeybees that store months-worth of honey, termites have a carpe diem approach to food safety, as they have no internal reserves. Instead, subterranean termites such as C. gestroi will relentlessly (and most of the time successfully) forage for new food sites to prevent food shortage in the first place. But if starvation of the termite colony actually occurs, then the colony just doesn’t have much of a survival strategy. Give it about 30 days.”
1 Chouvenc, T. (2019). Limited survival strategy in starving subterranean termite colonies. Insectes Sociaux. 10.1007/ s00040-019-00729-5.
2 Chouvenc, T. (2019). In a cannibalistic society, it’s not about survival – it’s all about recycling. Insectes Sociaux. October 24, 2019.