Funeral or Feast: How Termites Manage Their Dead
By Ed Ricciuti
The dead, so goes the saying, tell no tales. Except, that is, for eusocial insects—notably bees, ants, and termites—which communicate with colony mates after death. Just how termites do it is revealed in a new study published in January in the Annals of the Entomological Society of America: Dead termites give off pungent chemical signals that tell their colony’s undertaker-workers how to best handle their corpses for the good of the community.
A typical termite colony could look like London during the Black Death if it did not have undertakers to keep the corpses from piling up. Undertakers dispose of corpses in one of two ways: by burying them or eating them, although they treat the dead somewhat differently according to caste (reproductives, workers, and soldiers). The response of the undertakers to the caste depends on the chemical transmissions from the dead, the study shows.
The study focused how caste influences the burial behavior of eastern subterranean termites (Reticulitermes flavipes), notorious wood chewers that are the most widely distributed termite species in North America. A colony of 5 million of them can lose 70,000 members a day from natural causes. Left to rot, all those cadavers would spawn disease that could threaten the colony’s survival. By eating or burying the dead, undertakers not only keep the colony healthy but wear a second hat, as environmentalists that recycle precious nutrients.
A colony of eusocial insects—bee and ant colonies also have undertakers—can be considered a superorganism and, says senior author Xuguo “Joe” Zhou, Ph.D., of the University of Kentucky’s entomology department, to keep it functioning, termites are “guided by a series of algorithms [rules], including developmental, behavioral, and genetic … which can minimize potential risks.”
Using a simplified laboratory substitute for a nest and termites collected from a national forest, Zhou and colleagues examined the behavioral responses of the workers toward corpses from different castes and profiled the chemical “signatures” of the corpses. They documented their hypothesis that workers respond differently to corpses from different castes.
The chemicals released by the corpses are fatty acids, including 3-octanol and oleic acid, a sign that death was recent, and 3-octanone, which is produced later. These are among the chemical compounds believed to act as signals by which eusocial insects recognize death.
Worker corpses gave off higher amounts than soldiers of 3-octanone and 3-octanol, released at death and then diminishing over time, the study found. Neither of these chemicals was detected in nymphs of various types destined to reproduce, although the absence could be caused by limits on the detection of trace amounts during the experiments. Oleic acid, which builds up slowly after death and signifies that the corpse has lain around for a while, was detected in all castes, although it accumulated more slowly in soldiers.
Despite the differences in chemical signatures, undertakers consumed the corpses of all castes up to 64 hours after death. It makes sense from a survival standpoint because, say the researchers, “When left to decompose further, the corpse would become too depleted of nutrients or risky to be recycled.” Moreover, for a termite, a fresh corpse is like a vitamin supplement. “Given that wood is notorious for its imbalance of carbon:nitrogen ratio (ranging from 75:1 to 247:1), consumption of freshly dead individuals would provide an important nitrogen resource for wood-feeding termites,” the paper notes. Not surprisingly, fresh corpses observed in the study were always cannibalized, never buried as were decomposing remains.
Caste made a difference in burial behavior. Undertakers buried dead workers immediately, while soldiers were either buried or walled off. The latter behavior mirrors how workers wall off ingress points where soldiers are killed while defending the colony.
It took undertakers longer to find dead reproductive nymphs than workers or soldiers, and soldiers longer than workers. The researchers suggested that rapid response to workers is linked to the fact that they are by far the most numerous caste, by a factor of hundreds or more, and their labor is often risky. Simply put, in sheer numbers, workers are so dominant that their worker corpses deserve fast attention.
“Workers carry out almost all tasks within the colony except reproduction,” the paper notes. “The downside with riskier tasks, such as foraging and undertaking, is the higher turnover rate in termite workers. Consequently, equipped with a battery of early and late death cues, termites are able to manage corpses from the numerically dominant worker caste in a timely and efficient manner to maximize colony fitness.”
Annals of the Entomological Society of America
Ed Ricciuti is a journalist, author, and naturalist who has been writing for more than a half century. His latest book is called Bears in the Backyard: Big Animals, Sprawling Suburbs, and the New Urban Jungle (Countryman Press, June 2014). His assignments have taken him around the world. He specializes in nature, science, conservation issues, and law enforcement. A former curator at the New York Zoological Society, and now at the Wildlife Conservation Society, he may be the only man ever bitten by a coatimundi on Manhattan’s 57th Street.