The Venus flytrap – also known as Dionaea muscipula – is a rare plant that eats small living creatures as prey. Insects and spiders are among its favorite foods. But how does it know when to snap shut?
If you touch a Venus flytrap with a stick, you can probably get it to shut. But your stick won’t fool the plant into completing the process of digestion.
That’s because each Venus flytrap can close only half a dozen times over the course of its lifetime – so a Venus flytrap is particular about what it decides to digest. In fact, the traps have evolved to ensure that only worthwhile prey will trigger digestion.
How does it work? The answer lies in the construction of the plant itself. Every Venus flytrap has delicate hairs on the inside of its flat leaves. These hairs have to be disturbed twice in 20 seconds in order for the plant to close. The trap closes only when an insect or spider crawling along the leaves comes into contact with one or more of the hairs twice in succession.
But even this double stimulus of the hairs on its leaves won’t ensure the process of digestion in a Venus flytrap. Once its outer leaves have closed, the Venus flytrap has to be continuously stimulated by its struggling prey for the digestive process to continue. If there is indeed live prey in the plant, the trap seals around the insect and secretes its digestive juices.
So you might be able to get a Venus flytrap to close around a piece of rubber or a rock. But the plant knows better than to spend time digesting this object.
On the other hand, if a Venus flytrap does successfully absorb its prey, digestion will proceed. In that case, the plant will be open for business again … a few days later.