When an insect brushes the tiny trigger hairs inside a Venus flytrap, the trap can snap shut in less than a second. In a study published in Science, researchers proposed that the plant can move so quickly because its leaves are already under tension. A rapid change in the outer layer of the leaf may be enough to set that stored energy in motion.
To find out what sets off the snap, the team compared two explanations. One was that water rushes into cells on the outside of the trap, making them swell. When the researchers measured how quickly water entered those cells, the process took about 30 to 150 seconds. That was too slow to explain the snap. The experiment tested one route for water to enter the cells, leaving open the possibility of a faster route.
The team then tested how easily the outer cells could be deformed before and after the trap was triggered. The cells became easier to deform soon after the trigger hairs were touched. From these measurements, the researchers estimated that the cell walls became about 30 to 40 percent less stiff. This gave them a clue to how the trap could move so fast.
Study co-author Yoël Forterre compares the open trap to a spring held under tension. In the team's explanation, the outer cell walls soften just enough for the leaf to bend. The tension already stored in the leaf then drives the two sides together in a single snap.