What do you think of this fact?
Plants can’t count. Except this one, apparently. The Venus flytrap keeps track of how often its prey touches it, and uses that number to decide what to do next.
One touch could be a false alarm
Each half of the trap has three sensitive trigger hairs. When something brushes one of them, the plant fires an electrical signal, but nothing happens yet. As the University of Würzburg puts it, one signal could be a false alarm after all. According to Science News Explores, this keeps the trap from closing on a raindrop or a leaf brushing past.
If a second touch follows within 20 seconds, the trap snaps shut. So the number for closing is 2. If whatever got caught then stays still, the trap reopens after about half a day.
Five touches mean dinner
A trapped insect rarely stays still. A panicking one can hit the trigger hairs up to 60 times per hour, and the plant counts along. A team led by biophysicist Rainer Hedrich found that at 5 or more signals, the flytrap switches on the genes for digestive enzymes in all of its 37,000 glands. The third and fourth touches had no visible effect. The more touches, the more molecules the plant makes to absorb nutrients, which hints at a bigger meal. The study appeared in the journal Current Biology.
PhD student Jennifer Böhm also showed that one gene switched on by touch encodes a channel that transports sodium.
Bonus fact: According to the University of Würzburg, the flytrap remembers the number of touches for at least four hours.
So the harder an insect struggles, the more the trap gets ready to eat it. Terrible deal for the fly.