Plants, it seems, have an ear for danger. According to recent research, at least some of those seemingly inert organisms can tell when they're being eaten alive. They home in on the sound vibrations caused by munching insect mouths and respond accordingly±with a surge of chemical defense.
As Modern Farmer writes, "It’s a far more dynamic defense than scientists had realized: the plant is more aware of its surroundings and able to respond than expected."
Researchers recorded the noises of caterpillars eating leaves from Arabadopsis, a plant related to broccoli, kale and cabbage. (It goes by the common name thale cress.) Then, they played that horrifying noise back to other Arabadopsis plants. Plants exposed to those danger sounds produced significantly higher levels of defensive chemical compounds used to ward off insects than plants exposed to recordings of silence, the wind blowing or insect songs.
The researchers have no idea whether other plant species have the same or a similar sensory capability or how the thale cress manages to sense those vibrations in the first place. However, as Modern Farmer points out, the finding does raise some interesting questions about whether it might be possible to tickle crops into producing their own chemical defenses—as well, perhaps, about the ethics of vegetarians inflicting cruelty on their salads.