Baby butterflies use rhythm to trick ants into caring for them

Baby butterflies keep their beat to trick ants into taking care of them

By Meghan Bartels edited by Andrea Thompson

Some wily caterpillars take an unusual approach to ensuring they live long enough to become a butterfly: each one convinces an ant to carry it into the ant’s nest, providing food and shelter. Now scientists have found that these caterpillars use a surprisingly complex rhythm as a secret knock to convince the ants to come and get them.

This is shown by research published on 25 February i Annals of the New York Academy of Scienceswho found that caterpillars can sustain a stroke called a double meter that has so far only been identified in a couple of primates, says co-author Chiara De Gregorio, who studies animal behavior at the University of Warwick in England. It was very exciting, she says.

De Gregorio studies primates more regularly than insects, but her focus is on how rhythm shapes communication. She expanded to insects when colleagues approached her and noticed that these caterpillars somehow internally generated vibrations that seemed to mimic the pitch of an ant queen. (The ants rub together hardened parts of their abdomens to create their vibrations, but scientists aren’t yet sure how the larvae accomplish the feat.) The researchers wondered if the larvae might have matched the ants’ rhythm as well.

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So the researchers went out to the field in northern Italy and collected nests from two groups of ants, as well as larvae from nine species of butterflies that were related to each other but had shown varying degrees of association with ants – some required absolute care from ants to survive, others were happy to be taken in, the rest had no connection and could fend for themselves.

The researchers then recorded the vibrations each animal made. Amplified to reach a human ear, they only sounded like noise, but using acoustic analysis software, De Gregorio and her colleagues were able to analyze the rhythms created by each insect.

All the insects that the researchers analyzed were able to maintain a steady pulsating beat that the researchers call isochrony. “We were already shocked to find a really common metronomic isochronous signal,” says De Gregorio. “We thought, ‘Oh, that’s really cool.’

But what was even more surprising was that both the ants and the caterpillars that required their care also created a much rarer rhythm called double meter, where one beat lasts either twice or half as long as the beat that follows it. So far, says De Gregorio, researchers have yet to observe double meter in birds and have only found it in the vocalizations of a couple of primate species.

She and her colleagues hope to follow up with more experiments on these insects, specifically manipulating larval uptake to understand how the ant’s tendency to rescue larvae varies with summoning.

Overall, De Gregorio hopes that the discovery emphasizes the role of rhythm in communication. “The more we study rhythm, the more we see (it) in so many different animal species,” she says. “Evolution works in really weird and funny ways.”

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