In North America, termites cause more than $5 million in damage each year. Eastern Subterranean termites are the most widely distributed and most common encountered termite pest in North America. With colonies that can grow to the size of 5 million individuals and assuming a death rate similar to comparable termite species, it is estimated that as many as 70,000 termites could die in colonies each day. Corpse removal, a duty performed by worker termites called “undertakers” is extremely important for colony health. The longer a termite corpse remains, the greater the chances for disease spread. So, undertaker behavior (removal and disposal of dead termites), performed by worker termites, is extremely important for colony health.
Eastern Subterranean termites have developed two distinct behaviors to deal with dead nestmates: cannibalism and burying the dead. Cannibalism or eating the dead, provides an important service to the colony by recycling nutrients back in the colony. Wood, which is the primary food for Eastern subterranean termites is notoriously lacking in nitrogen. By eating the dead, nitrogen-rich material from the corpses is recycled back into the colony. Additionally, gut symbionts, necessary for digesting cellulose may also be recycled. Burying behavior, on the other hand, ensures that the threat of entomopathogens and subsequent disease is eliminated from the colony, which is especially important for eusocial insects living inside the closed system.
When a termite dies is begins to emit certain chemicals as it decomposes, including airborne volatile compounds such as 3-octanol and 3-octanone are released. This tells the workers that they are dead and they need to be taken care of. These chemicals do not persist for long and dissipate over time. Fatty acids are also produced, which are persistent. These chemicals build up in the corpse over time. The relative amounts of these chemicals in a termite corpse can provide information to undertakers to help determine what to do with the dead termite. New corpses were eaten if they were less than 64 hours old (higher levels of 3-octanol, 3-octanone) lower levels of specific fatty acids.
As a part of a series of laboratory experiments Jizhe Shi and his colleagues at the University of Kentucky learned the following information. Based on the levels of these chemicals encountered by undertaker termites (lower levels of 3-octanol and 3-octanone, and higher concentrations of fatty acids) older corpses were dealt with in two ways: either burying or walling off. All “old” worker corpses were buried or covered up with sand particles, feces, or other materials soon after discovery.
Interestingly, soldier termites were buried 50% and walled off about 50% of the time. When walled off, the entire tunnel to the chamber in which the dead soldier termites were present was blocked off. This behavior seems to be adapted for situations in which the colony is breeched by invading ants/termites and large numbers of dead soldiers remain. Workers instinctively block off that entire area because it’s perceived as unsafe, and the dead termites present there serve as reminder of danger if the area is opened up in the future.
It is notable that workers produce greater amounts of 3-octanol and 3-octanone upon death and were dealt with more quickly than soldiers. The authors of the study hypothesized that this was because of the greater proportion of workers present in the colony compared to other castes. Due to sheer the numbers present, workers need to be cleaned up first.
So, what does this mean for termite control? At first glance, the practical implications for our industry might not seem obvious – because they aren’t. This research does tell us that termites are not using visual cues like we might to determine the age of a corpse. Remember when the gang from the Goonies found One-Eyed-Willie on his ship while being chased by the Fratellis? They knew One-Eyed Willie was dead by looking at him, not sniffing him. Termites would have used chemical cues instead to know that he needed to be buried and not eaten.
This is the kind of research that might be categorized in the “cool to know” category, but it could actually impact on-the-ground pest control in the future. By having a better understanding of how termites deal with their dead, the cues they use, and the behaviors those cues elicit, one could imagine how this knowledge could be used to enhance termite exposure to biological or chemical control products in the future.
This research was recently published in the Annals of the Entomological Society of America based on work performed by Jizhe Shi and his colleagues at the University of Kentucky working in Joe Zhou’s lab. Find out more about this research here: Managing Corpses from Different Castes in the Eastern Subterranean Termite
Jim Fredericks, PhD, BCE