How Caterpillars Use Rhythm to Win Protection From Ants

Some butterfly caterpillars get through their most exposed stage of life by enlisting ants as guards, carers and even cohabitants.

Fresh research indicates that chemistry is not their only tool. They also create precisely timed vibrations: small rhythmic signals that apparently “sound right” to ants, allowing the caterpillars to secure protection, food and, in certain cases, entry directly into an ant nest.

In research led by scientists at the University of Warwick, the team reports that caterpillars can make accurate, organised vibration patterns that closely mirror the rhythms ants use for communication.

The discovery brings another dimension to an association that has intrigued biologists for years: the close, and at times strange, partnerships between ants and other organisms.

Caterpillars raised by ants

The early stages of life are perilous for many animals, and some butterflies face particular risks. During their caterpillar stage, certain species live in close association with ants and depend on them to stay alive.

Ants can behave as though these caterpillars belong to their colony. They may take them into the nest, defend them against predators and, in some instances, feed them.

Caterpillars generally offer something in return. Some release sugary substances that ants consume. Others take the arrangement further, acting in ways that help them fit in and, effectively, pass as “one of us” for long enough to escape attack.

Chemical mimicry has traditionally been the main explanation for this ability. Many caterpillars are believed to copy the scent signals on which ants depend, enabling them to get beyond the colony’s defences. However, the new study suggests scent is not the complete explanation. Vibrations also have a role in the world of ants.

The power of rhythm

Ant nests are dark, active environments, full of continual movement, contact and vibration. In such surroundings, a signal delivered at the right moment could be an effective means of attracting attention.

The research examines vibroacoustic signals: minute vibrations transmitted through plants, soil or the structure of an ant nest.

They are not “sounds” as people usually understand that term, but they work in a comparable way. They convey information through a shared setting, and ants are able to perceive them.

Dr Chiara De Gregorio, a research fellow in the University of Warwick’s Department of Psychology, characterises this as a form of communication between species in which timing is crucial.

“These caterpillars are essentially speaking the ants’ language – not just chemically, but rhythmically. By matching the ants’ beat, they can convince them they belong,” she said.

“Rhythm is a fundamental part of human life: we dance to it, clap to it, and instantly notice when something feels out of time.”

Complex rhythm was once considered to be restricted to primates, but researchers are enthusiastic about evidence that ants and caterpillars likewise maintain precise beats to communicate and survive.

Do caterpillars sound like ants?

To test whether caterpillars were truly generating rhythms like those of ants, the researchers examined signals from two ant species and nine caterpillar species.

Not every caterpillar in the study was equally focused on ants. Some had strong, dependent connections with them, while others had only limited associations or none whatsoever.

That range mattered because it allowed the team to pose a simple question: do caterpillars with a heavy reliance on ants “sound” more like ants?

Rather than merely recording whether vibrations occurred, the scientists examined rhythm in detail. They assessed characteristics including pulse tempo, the intervals between pulses, and the regularity or predictability of each pattern.

Stronger ant ties mean tighter timing

The results were notable. Caterpillars showing the greatest myrmecophily – the strongest associations with ants – generated the most consistent and most structured rhythms.

Their signals featured complex arrangements that researchers liken to musical rhythms, including alternating strong and weak beats. By contrast, caterpillars with weak ant links, or no ant relationships, generally produced simpler and less reliable signals.

Put another way, the more a caterpillar’s survival relies on ants, the more closely it appears to regulate its timing.

Rhythms that make the difference

The study identifies two rhythmic features that appeared especially significant. The first is isochrony: evenly separated pulses that create a stable, regular beat. A metronome provides a familiar example.

The second is double meter, a more elaborate pattern that switches between long and short intervals. It is more like a “one-two, one-two” sequence than an unvarying tick-tick-tick.

This pairing was found only in ants and in caterpillar species with the greatest dependence on ants. Such an overlap points to more than chance.

It suggests that these species may have developed coordinated rhythmic patterns because their lives have been linked so closely for such a long time.

Precision inside the colony

Professor Francesca Barbero, of the Department of Life Sciences and Systems Biology at the University of Turin, highlights the practical benefit. Accuracy is useful when an organism needs to be recognised inside a busy nest.

“In the dark, crowded environment of an ant nest, where constant vibrations and noise are unavoidable, precise rhythm may help signals stand out and be recognized quickly,” she said.

“For caterpillars, getting the rhythm right can be vital: it may determine whether ants provide care and protection, or ignore them completely.”

The consequences are easy to picture. A caterpillar that is accepted obtains an entire defensive system. One that is not may be regarded as an intruder – or, worse still, as food.

Rethinking rhythm and intelligence

A broader implication concerns rhythm itself. People often view rhythm as an “advanced” ability associated with music, language or large brains.

Research on animals has similarly tended to highlight complex rhythm in primates and a small number of other species celebrated for their cognitive abilities.

This research challenges that assumption. Ants and caterpillars are not associated with large brains, yet they may still employ sophisticated timing as a way to communicate, with genuine implications for survival.

Communication using multiple signals

The results also deepen the wider understanding of animal communication. It is seldom limited to a single channel: many species combine chemical, visual, tactile and acoustic cues.

The caterpillars examined in this study seem to do precisely this, using chemistry to fit in while employing vibration and rhythm to strengthen that message.

There is also something gently amusing about the image offered by the researchers.

Somewhere beneath our feet, amid the dark activity of an ant nest, a caterpillar may be “performing” a rhythm that preserves its safety. It does not do so for enjoyment of the beat, but because that beat may decide whether it is cared for or ignored.

The work was published in Annals of the New York Academy of Sciences.