Sylvia Cremer

ScienceShot: Marked for Death

In any colony of the ant Cardiocondyla obscurior, there's only one ergatoid—a dominant, wingless, adult male—and he's a vicious dictator. Researchers have previously shown that the reigning ergatoid will smear secretions on any adult wingless male that enters the nest, targeting him for death by worker ants. But new observations reveal that the ergatoid's aggression doesn't stop there. Researchers have found that adult ergatoids can sense when an unhatched pupae contains a wingless male, rather than a female or worker ant. They'll spend more time near that pupae, and initiate a fight—similar to the one shown here—soon after the ant hatches. Targeting newborns pays off: in fights between adult and newly emerged ergatoids, the adult won every fight. But if the younger ant was 2 days old, with its outer layers beginning to harden, it had a 14% chance of winning, and in 43% of these fights, both ants perished, rather than just the youngster. The team additionally showed that chemical signatures of ergatoid pupae and hatchlings are distinct from other classes of ants in the colony, explaining how adults can pick out which newborns to fight. The study, published today in BMC Ecology, explains one way that the balance of the colony is maintained to maximize the number of worker ants and females that keep the population large and functioning.

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