How Plants Make Sound—Ultrasonic Clicks You Can't Hear

The Silent Screams in Your Garden

Plants have long been considered the silent kingdom. They don't roar, chirp, or howl. But a growing body of research reveals they are far from quiet. When stressed by drought or physical damage, plants emit rapid bursts of ultrasonic clicks—sounds too high-pitched for human ears but detectable by specialized microphones and, crucially, by insects.

The field of plant bioacoustics has exploded in recent years, upending assumptions about how organisms in an ecosystem share information. What scientists have found suggests that the botanical world has an acoustic dimension we never suspected.

How the Clicks Are Produced

The sounds originate inside a plant's xylem—the network of narrow tubes that transports water from roots to leaves. Water travels upward through these vessels under tension, pulled by transpiration at the leaf surface. When a plant becomes dehydrated, that tension can exceed a critical threshold.

At that point, tiny air bubbles form inside the xylem conduits—a process physicists call cavitation. The bubble expands rapidly and the water column snaps, releasing stored mechanical energy. The vessel walls vibrate, and the result is a brief, sharp click. Each pop lasts only a fraction of a second, but a single stressed tomato plant can produce 30 to 50 clicks per hour.

The sounds fall in the 20–100 kilohertz range, well above the roughly 20 kHz ceiling of human hearing. Researchers at Tel Aviv University recorded them using ultrasonic microphones placed several metres from the plants, confirming the clicks are airborne—not just vibrations trapped in tissue.

What the Sounds Reveal

A landmark 2023 study published in the journal Cell by Itzhak Khait and colleagues demonstrated that these emissions are not random noise. The team trained machine-learning algorithms to classify recordings and found that software could distinguish between drought-stressed plants, cut plants, and healthy controls with high accuracy.

Different stresses produced distinct acoustic signatures. Water-deprived tomato plants ramped up their clicking before any visible wilting appeared, peaked around the fifth day without water, then fell silent as the plant dried out completely. Cut stems produced a different burst pattern. Even the species mattered: the frequency profile of tomato clicks differed from that of tobacco, wheat, or corn, partly because xylem vessel diameter affects resonance frequency—wider tubes produce lower-pitched pops.

Insects Are Listening

The most striking implication is ecological. A 2025 study published in eLife provided the first evidence that an animal species responds to plant sounds in a natural context. Researchers found that female Egyptian cotton leafworm moths avoided laying eggs on tomato plants that were emitting stress clicks. Given a choice between a clicking, water-stressed plant and a quiet, healthy one, the moths consistently preferred the silent host.

This makes evolutionary sense. A dehydrated plant is a poor food source for caterpillars. By eavesdropping on acoustic cues, moths can assess host quality without touching the plant. Scientists estimate these ultrasonic clicks could be detectable by insects at distances of up to five metres.

Researchers caution that this is eavesdropping, not communication. The plants are not "trying" to signal insects. Cavitation is a passive physical process. But the ecological effect is real: sound carries information, and natural selection has apparently tuned at least some insect ears to exploit it.

Why It Matters

The practical implications stretch from farm to lab. If affordable ultrasonic sensors can detect crop stress days before visible symptoms, farmers could irrigate more precisely, saving water and improving yields. Pest-management strategies might also benefit: understanding how insects choose host plants through acoustic cues could open new avenues for non-chemical crop protection.

More broadly, plant bioacoustics challenges the neat boundary biologists once drew between the "communicating" animal kingdom and the "passive" plant world. Plants may not have nervous systems, but the physics of their plumbing produces a rich acoustic landscape—one that the rest of the ecosystem has been tuning into all along.