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Dead or alive? Living ants chemically signal their vitality

dead ants, not dead, aliveAnts are notoriously efficient in their undertaking, carrying off their dead nestmates before the corpses can infect the colony with their pathogens. But how do the worker ants responsible for shuttling their deceased comrades' bodies out of the nest tell live ants from dead?

Some researchers had hypothesized that ants were able to detect breakdown products in decomposing bodies, but a new study in this week's online edition of the Proceedings of the National Academy of Sciences USA contends that the mechanism is just the opposite: While alive, ants produce chemicals that signal their vitality, signals that quickly vanish on death. In other words, deceased ants are identified by the absence of signs of life—a sort of chemical pulse falling silent—rather than the presence of signs of death.

Entomologists from the University of California, Riverside, found that Argentine ants—harvested from a citrus grove on campus—were able to detect dead nestmates before decomposition could truly have taken hold. Two chemicals produced by the ants, however, dolichodial and iridomyrmecin, curb necrophoresis, the removal of dead colony members, among fellow workers. (Or, as Discover's 80 Beats blog put it, the chemicals sound the famed Monty Python refrain, "I'm not dead yet!")

Dolichodial and iridomyrmecin dissipate quickly after death, plummeting to below half-strength in just 10 minutes. The two chemicals appear to serve as signals that repress necrophoric behavior in workers that come across living nestmates.

Photo courtesy of Dong-Hwan Choe

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