Plants Release Ultrasonic 'Screams' When Stressed

Humans have long assumed that anything which lacks a brain also lacks the capacity to feel and think. It's the reason people felt and thought that boiling crabs alive ended in a painless death, according to Phys.org. But in 2015, researchers cast massive doubt on that theory by delivering electric shocks, which made the crustaceans quite crabby.

Generally speaking, humans view plants as even more painlessly brainless than crabs. Just think about the term "vegetative state." When you're crabby, you're cranky, but as the New England Journal of Medicine explains, "Patients in a vegetative state show no evidence of sustained, reproducible, purposeful, or voluntary behavioral responses" to external stimuli such as touching. They also have zero awareness of themselves or the outside world despite having sleep-wake cycles.

Well, it turns out that plants may not be as unresponsive to the world as humans thought. We'd say that vegetation had the last laugh by exposing human ignorance. But they'd probably have a hard time laughing, not because plants lack vocal cords but because humans made them scream from stress.

If a tree lands in the forest, but no one is around to hear it, does it make a sound? That answer might depend on how upset the tree was about falling. In 2019, Live Science reported that at least some species of plant seem to release "scream[s]" at frequencies humans can't hear when placed under duress. Scientists at Tel Aviv University subjected tomato and tobacco plants to physical stress and measured their reactions with a microphone.

One set of test subjects was forced to endure a drought, a second got snipped, and a third served as a control group and wasn't touched at all. The researchers found that "drought-stressed tomato plants emitted about 35 ultrasonic squeals per hour, on average, while those with cut stems made about 25." Tobacco plants emitted 11 and 15 screams respectively under those conditions. Meanwhile, the plants that got left alone averaged less than one squeal an hour.

The idea of torturing a tobacco plant may seem like sweet revenge for lung cancer, but it might also mean that plants have to sit by helplessly as you kill their brethren and smoke their remains like an unwilling Tupac. It's unclear how many kinds of plants react this way to stress, but it seems that trees scream, too. Per Smithsonian, in 2013, researchers found that drought-stricken arbors make ultrasonic sound that experts interpreted as "cries for help." So logging is probably a tree's version of a Saw movie.