Provoking a Venus flytrap takes a certain amount of finesse. If you brush just one of the trigger hairs inside of its leaves, the plant likely won’t react. But if you trigger it again quickly enough, it will spring into action, swinging its famous mouth shut.
Waiting for a double trip probably keeps the plant from wasting energy on raindrops or other things that aren’t nutritious flies. But despite centuries of interest in the species, no one was quite certain how the plants remember the first trigger in order to act on a second.
In a paper published last week in Nature Plants, researchers reported they had found the cause: calcium ions. By inducing the flytraps to glow when calcium entered their cells, a team of scientists was able to show how the ions build up as the hairs are triggered, eventually causing the snap.