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How Ants Respond to Predators Suggests Superorganism Capabilities

ByEben BeinNOVA NextNOVA Next

When you accidentally pick up a burning hot plate of dinner from the microwave, despite the ensuing stream of expletives, you are unlikely to sustain a severe burn. While a few cells in your hand may die, the rest of your cells coordinate to protect you by letting go of the plate and yanking your hand out harm’s way. With even less swearing, some ant colonies can achieve a similar level of coordination—losses from different parts of the colony can trigger the rest to retreat from danger.

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Entomologist Thomas O’Shea-Wheller studies these behaviors in colonies of

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Temnothorax albipennis ants in his lab at the University of Bristol. When he simulates predator attacks, he said the ants “are able to communicate the location of where it is happening very precisely,” and thus execute the most effective escape. When attacked outside the nest, they retreat inside, while if attacked from the inside, they jump nest and search for a new home.

To obtain test subjects for his most recent study , O’Shea-Wheller and his colleagues head to a quarry several miles out of town and use small straw-like tools to suck ant colonies into test tubes. T. albipennis colonies are only a few hundred individuals at most—a relatively manageable size. Back in the lab, they provide each colony with a transparent nest through which they can observe nest maintenance workers as well as scouts running reconnaissance for food and new nesting sites.

However, sometimes the scouts never make it back. O’Shea-Wheller, paintbrush in hand, sweeps them into another container, as though he were a pheasant pecking away at a delicious lunch. Within minutes, the outbound stream slows to a trickle and stops.

Related ant species do this by monitoring how frequently those in the nest are jostled by returning scouts. According to Oxford zoologist Takao Sasaki, if nobody bumps into them on the way in, the colony ceases sending out scouts, thereby avoiding a waiting predator. Sasaki’s colleague at Stanford, Deborah Gordon, demonstrated this by removing scouts but mimicking their return by dropping small glass beads into the colony entrances. Those colonies were tricked—they continued to send out scouts.

But lock-down isn’t the ants’ only strategy. Several of O’Shea-Wheller’s synthetic nests have holes through which he can slip a paintbrush, simulating a smaller predator in the nest. The moment an ant detects the brush, it will become “very excited, kind of run around making a commotion,” O’Shea-Wheller said. Neighboring ants respond in kind; some may even grab a brush bristle in their tiny jaws and try to sting it. In a matter of seconds, the “whole colony will explode into activity.” The ants likely sound the alarm by releasing a pheromone called dimethalpyrazine, which other ants can detect and release themselves, activating the entire colony via a chain reaction. Workers pick up the defenseless larvae and evacuate. Over the next hour or two, the entire colony migrates to another synthetic nest laid out about a foot away.

To O’Shea-Wheller, the ability to coordinate different responses to these two types of attacks is part of what makes them a super-organism—a disconnected but unified living thing—rather than just a group of individuals. The distinction is clear “if you were to compare to something we wouldn’t call a superorganism, like wildebeests,” O’Shea-Wheller said. “If they’re being attacked by predators, they’re quite uncoordinated.”

But Sasaki, is not so sure. While he loves the study, he questions whether the spatial coordination is actually unique. If he were to try a similar experiment on a flock of starlings, removing individuals from the periphery and the center, he said. “It’s plausible I’d find similar results…but I wouldn’t call them a superorganism.”

To him, it’s that “the goals are different,” he said. “Individual ants have goals to achieve collective tasks…they’re really altruistic. Some ants go outside even though it’s really risky…for pigeons, it’s selfishness.”

“But it’s tricky,” Sasaki said, acknowledging that the distinction between a group of organisms and a super-organism may be philosophical.

Photo credits: Animalparty/Wikimedia Commons (CC BY)

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