Hidden in the rainforests of French Guiana, scientists have recently discovered a species of termite with a secret weapon in its defensive arsenal, "something that is really outstanding," says Thomas Bourguignon, a researcher at Hokkaido University in Sapporo, Japan, who recently co-authored a Science paper on this unusual strategy. As Neocapritermes taracua workers age, they begin to produce blue copper-protein crystals that they store in external pouches on their backs. If, while grappling mandible-to-mandible with opponents, our termite heroes find themselves losing a fight, they can rupture their abdominal walls, most likely by contracting their abdominal muscles.
Then comes the really ferocious part: once the pouch has torn open, the blue crystals mix with saliva stored in the termite's nearby glands to create a toxic goo. As the sticky substance leaks from their "explosive backpacks" (a term making its debut in Science), the workers remain in the fray, coating and killing as many opponents as possible with the poison -- until it fells them, too.
"The sophistication" of this suicide strategy is "a new level of self-defensive weaponry," says Olav Rueppell, a biology professor at the University of North Carolina, Greensboro, and the author of a recent review on the self-destructive defense behaviors of social insects. Though termites are a familiar pest to homeowners -- their tendency to munch wood causes billions of dollars in property damage each year in the U.S. alone -- they’ve long been an enigma to scientists, partly because they’re hard to observe: they tend to dig nests in soil or rotting wood, sealing the exits behind them and rarely venturing out. Many species also live in remote regions where they don’t often come into contact with people.
Researchers estimate there are some 4,000 termite species in the world -- they exist on every continent except Antarctica -- but scientists have identified only about half of the ones they think are out there. Most of those species lack common names, and little is known about their biology or behavior. In fact, several years ago DNA testing revealed that, rather than belonging to their own order, termites should be classified as a cockroach family.
Yet researchers do know that N. taracua and other termites are eusocial -- a likely reason they’ve been able to evolve such selfless defense behavior. Like ants, bees, and wasps, termites live in communal societies in which each insect plays a specific role. Soldiers and workers are often sterile and can’t pass on their own genes. Instead, their efforts support the reproductive activities of the fertile "queens" and "kings" to whom they’re related. And among termites and other eusocial insects, it’s not unusual for an individual to risk its life to defend the colony. But suicidal self-defense, or autothysis -- in which defenders make the ultimate sacrifice in order to splash attackers with their own bodily juices -- is rare. Researchers have only observed autothysis in two genera of carpenter ant and a handful of termite genera. Of those, N. taracua is the only species known to mix chemicals in order to achieve an extra-dangerous concoction -- and to have evolved "such a complex device" in which to store and deploy its powerful potion, Bourguignon says.
Exactly how eusociality evolved, however, is a mystery. When Darwin confronted the question while formulating his theory of natural selection, he was initially stumped: if the traits that made organisms the most successful at reproducing were the most likely to be passed on to the next generation and the next, how could sterile creatures become so populous in eusocial societies? Darwin’s solution to this "one special difficulty, which at first appeared to me insuperable, and actually fatal to my whole theory," was that "selection may be applied to the family, as well as to the individual," he wrote in On the Origin of Species. In 1964, evolutionary biologist W.D. Hamilton drafted a theory of "kin selection" supporting this idea. According to Hamilton’s law, it makes evolutionary sense for relatives to sacrifice themselves for one another, since doing so helps protect the genes they hold in common.
Most species -- humans included -- exhibit the kind of "altruism" Hamilton’s law predicts. But eusociality in particular "has meant tremendous success where it has evolved," Rueppell says. Though few known insect species are eusocial, they tend to be particularly resilient -- as anyone who has tried to rid their yard of a fire-ant mound or a wasp nest can attest. Some estimates suggest ants make up as much as a fifth of the world’s terrestrial biomass, and there are more than 16,000 species of bee worldwide, as well as 145,000 kinds of wasp.
Though little is known about N. taracua’s lifestyle, Rueppell says the discovery of its unique autothysis technique is "an important step forward" in understanding what termites and other eusocial insects are capable of. So far, it seems survival of the fittest produces even more elaborate, innovative defense mechanisms when it’s practiced family-style.