Venus flytrap
© Hugo A. Quintero/Flickr
A Venus flytrap captures a lizard victim.

Venus flytraps and other carnivorous plants have the ability to count, according to a new study.

The discovery adds to the growing body of evidence that certain plants possess many animal-like abilities, even though they do not have brains. In this case, it's now known that meat-eating plants can count up to at least five.

As for why this would be useful, project leader Rainer Hedrich of Universität Würzburg explained: "The carnivorous plant Dionaea muscipula, also known as Venus flytrap, can count how often it has been touched by an insect visiting its capture organ in order to trap and consume the animal prey."

For the study, published in the journal Current Biology, Hedrich and his team used a machine to simulate an insect touching Venus flytraps. The machine emitted electric pulses to fool the plants into thinking an insect had just landed.

The researchers found that each numbered pulse/touch was associated with a particular response:

One: The plant's trap enters a "ready to go" mode, noting the stimulation.

Two: The trap begins to close around the source of the stimulation.

Three: The trap closes tightly.

Four: The plant produces a hormone associated with the feeding process.

Five: Glands on the inner surface of the trap produce digestive enzymes and transporters that help to take up nutrients. At this point, if the stimulation were a real insect or other victim, it would be dinner.

Hedrich describes the numbered steps as a "deadly spiral of capture and disintegration." The more the insect or other prey feels trapped, the more the plant closes in on the victim.

The process further benefits the hungry diner, because the plant doesn't immediately invest its resources in prey that could, at the earlier stages, escape, or that might be too small to bother with much.

"The number of action potentials informs (the plant) about the size and nutrient content of the struggling prey," Hedrich explained. "This allows the Venus flytrap to balance the cost and benefit of hunting."

A puzzling observation during the study was that the plants show a marked increase in production of a transporter that allows them to take up sodium. The scientists are not sure what salt does for the plant, but they suspect it has something to do with how carnivorous plants maintain the right balance of water inside their cellular walls.

To answer this question and others, the researchers are now sequencing the Venus flytrap genome. They expect it will reveal more about how the plants evolved to support their meat-loving ways.