Caterpillars Hear Without Ears

Caterpillars long regarded as simple, leaf-eating larvae have revealed a surprising sensory ability: they can hear. New research from scientists at Binghamton University shows that Manduca sexta caterpillars, commonly known as tobacco hornworms, detect airborne sound using tiny hairs on their bodies rather than ears.

The findings were presented in December 2025 at the joint meeting of the Acoustical Society of America and the Acoustical Society of Japan and published as a lay-language paper in the Proceedings of the Acoustical Society of America.

The discovery challenges conventional assumptions about how insects perceive sound and opens new avenues for understanding both animal behavior and bio-inspired technology.

Hearing Without Traditional Ears

Most animals that can hear rely on specialized organs such as eardrums or tympanal membranes. Manduca sexta caterpillars, however, have no such structures. Yet researchers had observed that the larvae respond defensively to certain sounds, raising questions about how they detect these signals.

“We knew these caterpillars were reacting to sound, but the mechanism was a mystery,” Sara Aghazadeh, a doctoral researcher at Binghamton University and one of the study’s lead authors explain in the journal report. “They don’t have ears, so we wanted to understand what sensory system was involved.”

The research team, which also included doctoral researcher Aishwarya Sriram, Associate Professor Carol Miles, and Distinguished Professor Ronald Miles, designed experiments to distinguish whether caterpillars were responding to airborne sound or to vibrations transmitted through the surface they were standing on.

In laboratory experiments, the caterpillars were exposed to controlled tones at two frequencies: 150 hertz and 2,000 hertz. These frequencies were selected because they fall within ranges commonly produced by environmental sounds and potential predators.

The researchers carefully measured how much the surface beneath the caterpillars vibrated and compared that with the caterpillars’ behavioral responses. The results were clear. The caterpillars were between 10 and 100 times more sensitive to sound traveling through the air than to vibrations in the substrate.

The Role of Sensory Hairs

To identify the specific sensory structures involved, the team conducted a second set of experiments. They removed fine hairs from the thorax and abdomen of the caterpillars and repeated the sound tests.

Once those hairs were removed, the caterpillars’ responses to sound dropped dramatically. Without the hairs, many of the larvae no longer reacted to the same acoustic signals that previously triggered defensive movements.

“The loss of sensitivity was striking,” the report told. “It showed that these hairs are essential for sound detection.”

According to the researchers, the hairs function as mechanosensors that bend in response to pressure changes caused by sound waves moving through the air. Those movements are then translated into neural signals, allowing the caterpillar to perceive sound despite lacking traditional hearing organs.

The ability to detect sound may offer caterpillars a crucial survival advantage in the wild. The researchers believe the larvae may be tuned to frequencies associated with predators, particularly parasitic wasps that prey on caterpillars.

Wingbeats from hovering wasps often produce low-frequency sounds in the same range detected during the experiments. Hearing these sounds could allow caterpillars to freeze, thrash, or drop from leaves to escape attack.

“From an evolutionary perspective, this makes a lot of sense,” Aghazadeh said. “Even a very simple form of hearing could provide enough warning to improve survival.”

Implications Beyond Biology

The findings may also have implications beyond insect biology. Understanding how caterpillars detect sound without ears could inspire new approaches in engineering, particularly in the development of ultra-small microphones and acoustic sensors.

Current micro-electromechanical systems, or MEMS microphones, often struggle to balance sensitivity with size. Biological systems like the sensory hairs of Manduca sexta offer an alternative blueprint.

“Nature has already solved many engineering problems,” Ronald Miles said. “These caterpillars show us that you don’t need a traditional eardrum to detect sound effectively.”

While the research does not suggest that caterpillars hear in the same way humans do, it broadens the scientific definition of hearing itself. Sound perception, the researchers argue, does not require ears—only a mechanism capable of detecting and interpreting pressure changes in air.

“This work reminds us that sensory systems can take many forms,” Aghazadeh said. “We’re only beginning to understand how diverse and creative evolution can be.”

As studies continue, scientists expect that similar mechanisms may be found in other insects and invertebrates, further reshaping how researchers think about hearing across the animal kingdom. (Wage Erlangga)