Research Results: Can Plants Hear Themselves Being Eaten?

My eight-year-old daughter REALLY loves animals. And not just animals in the traditional sense of the word, but also any insect or invertebrate which moves: ants, caterpillars, earthworms—you name it. She has come home from a day of 2nd grade and moped around in sincere mourning because some boy maliciously stepped on a creepy crawly on the playground during recess. Luckily, she has a pretty healthy disconnect between the animals she loves and the food she eats.

Despite her expressions of horror each time discussion ensues involving where the chicken nuggets or cheeseburgers in her favorite fast food meals actually come from, she still somehow manages to enjoy the nutritional benefits provided by many of her animal friends. And while not a vegetarian, she has always enjoyed a good salad, perhaps comforted by the thought that no animals were harmed in the preparation of a bowl of leafy greens. Leave it to science to almost deprive her of this comfort.

Plants React

Researchers at the University of Missouri discovered that plants can identify the sound of eating and react defensively in response. The sounds, or rather vibrations, made when caterpillars fed on the Arabidopsis plant triggered changes to the plant’s metabolism, increasing secretions of defensive chemicals (mustard oils) in the plant which naturally deter the caterpillars.

The research, led by Rex Cocroft and Heidi Appel, involved placing reflective material on the leaf of the plant and using a laser to measure any movement caused by the eating caterpillar. They were then able to expose another plant to a recording of the vibrations and found this plant produced more defensive chemicals than plants exposed to silence or vibrations from sources other than the predatory invertebrates. The researchers thus determined these plants could distinguish between the threatening chewing vibrations of caterpillars and vibrations from other environmental sources.

The fact that plant life can reflexively respond to external stimuli is not earth-shattering news; any living thing would be expected to respond to external stimuli in some form or another. What this discovery does not assert is that plants somehow feel pain or that this selective reaction to specific vibrations indicates sentience. The results of this study, which were published in the peer-reviewed scientific journal Oecologia, suggest only that plants can selectively distinguish between vibrations caused by different external stimuli and react to those which are threatening to the plants’ survival.

So lest you be deceived that you are causing pain and torment when you place a wad of fork-skewered, dressing-drowned leafy spring mix into your mouth, rest assured that scientists have made no such discovery. The act of giving human behavior, characteristics, or motivation to animals, inanimate objects, or natural phenomena is called anthropomorphism, which is precisely what has befallen the Arabidopsis plant, and—by generalization—all plant life, in the more creative headlines and accounts related to this experiment.

Bottom Line

Just as Chinese teenagers were not endowing fresh produce with anthropomorphic characteristics by leashing cabbages and taking them for walks to combat loneliness, scientists have not proposed that plants can literally hear (or talk) as some would have you believe. What researchers at the University of Missouri did discover is that plants can selectively distinguish between vibrations of external stimuli and react defensively to the sound of chewing by releasing extra chemicals to deter the offending caterpillars.