Butterfly Caterpillars Have Learned To Speak Ant, And Scientists Can Hear It

Some animals trick their way into ant colonies by smelling like ants. Certain butterfly caterpillars take that deception even further. New research shows that the most ant-dependent species don’t just copy chemical signals. They vibrate with the same rhythmic precision as their hosts, producing a beat pattern scientists had previously documented mainly in primates.

Ants communicate largely through vibration. Workers drum and scrape against soil and plant stems to coordinate rescues, recruit nestmates, and signal rank within the colony. For caterpillars that need ants to survive, sending the right vibration can mean the difference between being adopted and being eaten. What the new research found goes well beyond simple mimicry.

Some caterpillars have independently evolved a two-layered rhythmic structure called “double meter,” a pattern based on the timing between pulses, where some beats are roughly twice as long as others. Scientists had previously documented double meter mainly in singing primates like gibbons and orangutans.

Published in the Annals of the New York Academy of Sciences, the study examined signals from two ant species and nine butterfly species across a spectrum of ant-dependence, ranging from caterpillars with no relationship with ants at all to those that cannot survive without them. The closer a caterpillar’s ecological bond with ants, the more its vibrational rhythm resembled the ants themselves.

How Scientists Measured the Rhythm of Bug Communication

Researchers from the University of Warwick, the Forest Research Institute in Poland, and the University of Turin used recordings of caterpillars and ants collected in Northern Italy. Rather than simply asking whether the signals sounded similar, the team focused on the mathematical structure of the timing between each vibrational pulse.

Each time an insect signaled, the researchers measured the gap between successive pulses, then calculated the ratio of each gap to the one that followed. This let them detect whether the pulses were evenly spaced, a pattern called isochrony that works much like a metronome’s steady tick, or whether they fell into a more layered structure where some beats were roughly twice as long as others. That second pattern is double meter, the same underlying structure humans feel when tapping a foot to music.

Fifty-six recordings were analyzed, each from a different individual insect, with tens of thousands of pulse intervals measured across all species. Nine butterfly species were grouped into four categories based on their degree of reliance on ants: no association, low, medium, and high myrmecophily, a term for how deeply an organism’s life is tied to ants.

Ant-Dependent Butterfly Species Share a More Sophisticated Rhythm

Every species in the study, including caterpillars with no ant associations at all, produced signals built around that simple isochronous rhythm. That shared baseline suggests the steady-beat structure may be a basic feature of insect signaling that evolved long before any relationship with ants began.

Beyond that, though, the groups diverged sharply. Only ants and the most ant-dependent caterpillars, specifically Plebejus argus and Phengaris alcon, showed the added complexity of double meter. These are species embedded in ant colonies, entirely reliant on their hosts for food and protection. Their signals shared the same layered rhythmic structure as ants, and in some cases showed similar pulse tempos.

Phengaris alcon caterpillars infiltrate Myrmica ant colonies and manipulate workers by mimicking ant queens. Previous research had already shown these caterpillars can copy the acoustic frequencies of queens. The new data add another layer: their rhythmic timing is finely matched as well.

Caterpillars with a moderate level of ant-dependence produced only the simpler isochronous rhythm, and did so at a noticeably slower tempo. The researchers suggest this slower pace may be an energy-saving strategy for species that need to attract ant attention but cannot sustain more elaborate signaling. Species like Polyommatus coridon, which attracts ants largely by secreting nutritional rewards, may simply need a “good enough” signal rather than a perfectly matched one. Caterpillars with little or no ant association showed consistent, isochronous patterns that likely serve entirely different purposes, possibly mediating territory disputes or rival assessment among their own kind.

A Rhythm Pattern Rare Outside Primates

The double meter discovery is what makes this study stand out. Until recently, this particular rhythmic structure had been identified mainly in mammals, particularly singing primates. Gibbons, orangutans, and titi monkeys all organize their vocalizations around similar layered rhythm structures. Finding it in insects raises the possibility that certain temporal patterns may be so effective for communication that evolution lands on them independently across wildly distant branches of the animal kingdom.

The researchers are careful not to overreach. The paper notes the rhythmic complexity “is here interpreted as a temporal pattern rather than as evidence of perceptual or functional complexity.” The caterpillars are not necessarily perceiving rhythm the way a primate does. The resemblance likely reflects convergent pressure toward signal efficiency rather than any shared cognitive wiring.

What stands out is that the most ant-dependent species, the ones whose survival hinges on being accepted rather than expelled, are precisely the ones that developed this extra layer of precision. Ant signals, by comparison, were found to be less rhythmically regular, likely because ants use vibrations across many different behavioral contexts. A caterpillar’s signal has one job: get the ants to respond favorably. In that context, getting the beat exactly right matters.

A caterpillar hidden deep inside an ant nest, vibrating at exactly the right tempo in a colony that has already accepted it on chemical grounds, has pulled off something worth appreciating. It learned to speak a language not its own, in the dark, without vocal cords, using nothing but the scrape of its body against the ground.

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