In a colony of eastern subterranean termites (Reticulitermes flavipes), as many as 70,000 termites may die every day. Dealing with all those corpses is critical to colony health, and a new study reveals how the primary methods for termite undertakers—burying corpses or eating them—varies by caste. (Photo by Joseph Berger, Bugwood.org)
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.