Plants hear herbivores coming. No, really.

National Geographic reveals what really goes on in a plant’s… mind?… when sap-thirsty plant killers are on the prowl:

[University of Wisconsin researcher John] Orrock and botanist Simon Gilroy show that black mustard plants can “hear” the chemical signals of approaching plant-eaters—and prepare to fight back.

“One of the things that makes plants so ecologically interesting is that they can’t run away,” says Orrock. Forced by their immobility to get creative, plants have evolved a whole host of spectacular defenses—from thorns and poison darts to awful-tasting chemical juices—against would-be predators.

Orrock and Gilroy used water mixed with snail mucus to slime the soil at the base of a number of black mustard plants. (Because snails secrete a slimy trail of mucus everywhere they go, the presence of mucus is a sure sign to plants that a snail is nearby.) The team then offered the slime-exposed plants to hungry snails, along with a control group of un-slimed plants. As expected, the plants that had been “warned” by the simulated threat had already armed their defenses, and the snails left them alone. The oblivious plants in the control group weren’t so lucky.

To see if the mere presence of another snail’s mucus was enough to make a snail lose its appetite, the scientists also served two samples of store-bought cabbage: one treated with slime, and one un-slimed. The snails chowed down on both samples with equal gusto. Clearly, the living black mustard plants had something the dead cabbage didn’t: defense.

As amazing as that sounds, there’s more: When time passed and no attack took place, the plants let down their guards. By the time the plants were served up for snail snacks, those that had been slimed in the distant past had become tasty again. Those specimens that had been slimed more recently, however, were still ready for a fight.

[by the inimitable Ms Horowitz]