To catch a meal, a Venus flytrap counts to five

Think of a carnivorous plant and the first to pop into your head might be the human-devouring Audrey II of Little Shop of Horrors. But if you think of a real plant, there’s no better example than the Venus flytrap. The tiny plant, a native of the Carolinas, compensates for the nutrient-poor soils of its wetland home by trapping and consuming insects.

Unlike Audrey II, Venus flytraps can’t stretch out their stems to grab a meal. They are passive eaters and have to wait for their food to come to them. Once an insect steps into the trap, though — snap! — it’s quickly caught.

But a flytrap can’t just snap shut anytime something, like a drop of rain, touches it. It needs to close only when prey is inside. That’s because the process of shutting the trap and producing digestive enzymes consumes energy. And traps don’t last forever; they fall off after several closures or partial closures and have to be regrown. Too many false alarms and the plant won’t have enough energy to survive, let alone grow or produce seeds.

Scientists had figured out that it takes two taps, in rapid succession, on tiny sensor hairs within the trap to initiate closing. But then what happens? New research shows that a Venus flytrap needs at least three more touches to turn on the genes responsible for those insect-digesting enzymes. The study appears January 21 in Current Biology.

In short, the plant can count to five.

Jennifer Böhm of the Institute for Molecular Plant Physiology in Würzburg, Germany, and colleagues simulated the landing of an insect on the trap with an electrode and then monitored how the plants responded. After a first touch, the trap stayed open. At the second, it snapped shut. The next few touches simulated the prey struggling to escape the green “stomach” in which it had become entrapped. After a total of five taps, the glands on the inside of the trap received the message that they needed to start making enzymes to digest the meal.

Digestion itself takes five to 12 days, depending on the size of the meal. During that time, the plants scarf up carbon, nitrogen, phosphate and sulfur. The new study also found evidence that the plants consume sodium from their prey. The researchers aren’t quite sure what the plants use the sodium for, but it may help maintain water balance inside cell walls.

While the carnivorous nature of the Venus flytrap may make it a fascinating research subject, there is an even darker tale to be told. The plant is one of the many species threatened by poaching. It may seem odd that a plant here in the United States is threatened by poachers, especially since it’s so easily grown and cloned in the greenhouse. But every so often, there are reports of poachers caught with hundreds of tiny flytraps they intended to sell on the black market. (No one is quite sure yet who is buying the plants.)

The situation is so bad that conservationists warn the plant could soon become extinct in the wild. And with the number of wild Venus flytraps already dwindling because of shrinking habitat, removing those plants puts the species further at risk.