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Caterpillar uses chemicals to recruit ant bodyguards

By Brooks Hays
Caterpillar uses chemicals to recruit ant bodyguards
A caterpillar is guarded by its loyal cadre of army ants. Photo by Masaru Hojo/Kobe University

KOBE, Japan, Aug. 3 (UPI) -- A caterpillar species in Japan uses pheromones to turn ants into zombie bodyguards.

Until now, researchers thought caterpillars and ants were taking part in a fair exchange of goods for services. But as scientists reveal in a new paper, published in Current Biology, the transaction is stacked in the caterpillar's favor.

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Prior to the new research, scientists assumed ants were guarding the Japanese oakblue butterfly caterpillar on their own volition -- and that their services were paid for with a sugary syrup-like secretion.

But recently, scientists at Japan's Kobe University noticed that it was always the same ants guarding the caterpillar. If it was truly a free exchange, one would assume a multitude of ants would make the trek to trade a few hours of work for sugar.

Instead, the same few ants appeared to remain by the caterpillar's side, abandoning their daily activities.

The Japanese oakblue butterfly begins its life as a caterpillar. Its life, however, is divided by the process of metamorphosis. The caterpillar becomes vulnerable to predators like wasps and spiders during its transitionary period when it wraps itself in a cocoon inside the leaves of an oak tree. Fortunately, the caterpillar's power of chemical persuasion allows it to form a small army of aggressive bodyguards.

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Researchers studied caterpillar-ant interaction in the lab and found that, indeed, ants that sipped the caterpillar's sugary secretions were enticed to abandon their nests and stick by the side of the caterpillar.

Scientists also found that caterpillars seemed to trigger a frenzied attack behavior by inverting its tentacles. Ants that had not drank the caterpillar's potion did not react to the signal in the same way as their zombie peers.

The observations led researchers to conclude that the caterpillar is controlling and directing its bodyguards using a combination of chemical and visual signals.

"There are glandular cells near the tentacles that could be secreting chemical signals," researcher Masaru Hojo told New Scientist. "It is possible that both visual and chemical signals are stimulating the ant aggression."

"We conclude that DNO secretions of lycaenid caterpillars can manipulate attendant ant behavior by altering dopaminergic regulation and increasing partner fidelity," Hojo and his colleagues wrote in their paper.

But Martin Heil, a scientist at the Center for Research and Advanced Studies of the National Polytechnic Institute in Irapuato, Mexico, says that while the findings are illuminating, they're not necessarily proof that ants are losing out.

"The benefit for the caterpillar is obvious, but we do not know whether the benefit for the ants is as minimal as the authors argue," he told New Scientist. "If the liquid that the caterpillars secrete is sufficiently nutritious, then it might well be that the overall balance for the ants also is positive."

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Researchers at Kobe say their work has inspired them to reexamine other biological relationships that appear on the surface to be mutualistic.

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