How Does a Venus Flytrap Work?

Carnivorous plants enchanted Charles Darwin, who marveled at how they defy all expectations of proper plant etiquette. “This plant, commonly called Venus’ fly-trap,” Darwin wrote in Insectivorous Plants (1875), “is one of the most wonderful in the world.”

In his writings, Darwin noted the incredible speed with which the Venus flytrap shuts its traps. He observed how the plant uses these traps to absorb nourishment from insect prey, leaving only a dried out husk when it reopens its jaws over a week later. By painting little black dots on the traps, Darwin was even able to show how their surface layers contract and expand. But he didn’t fully understand the mechanisms by which the plant hunts and digests.

The Venus flytrap’s Habitat and Anatomy

Native to the coastal bogs and savannas of the Carolinas, Venus flytraps grow slowly and close to the nutrient-poor soil they inhabit. If you kneel next to a wild plant, you will likely see a circular arrangement of four to seven flat green stalks that end in blushing, toothed traps. While the broad, elongated stalks perform photosynthesis — the chemical process plants use to turn water, carbon dioxide and energy from sunlight into sugars and oxygen — the crimson traps wait around for insects, spiders or other critters they can seize for their nitrogen, which the plant needs to continue making vital proteins. (If large enough, the traps can catch small amphibians or rodents.)

The Design of the Traps

When a trap shuts, the long spiky hairs on the rims of the lobes interlock, but leave enough room for tiny insects to get out, so the Venus flytrap does not waste energy digesting an insignificant meal. The traps will open sooner if an insect manages to flee, but will close more tightly if the victim struggles.

Interestingly, rain rarely triggers the traps because the likelihood of a raindrop falling in exactly the same place twice in under 30 seconds is negligible — a good thing for the Venus flytrap, who would otherwise starve every time it rained.

How Electrical Signals Travel in Plants

Plant cells can generate electrical currents — action potentials — just like animal cells. In animals, these currents travel along a nerve cell’s main branch, the axon, which has evolved to efficiently conduct electrical impulses. But plant cells don’t have specialized structures for conducting electrical signals, so how do action potentials travel in plants?

According to Volkov, action potentials in plants may travel through phloem — living tissue that transports sugars and other nutrients through a continuous arrangement of tubular cells.

“Animals have neurons and axons,” Volkov said, “and plants have phloem — but the properties are very similar. In both cases you have a cell membrane. In both cases you have ion channels, which keep the propagation of the action potential constant. There’s a not a big difference.”

Plant Electrophysiology

“We’ve known about electrical signaling in plants for as long as we’ve known about it in animals,” said Elizabeth Van Volkenburgh, a botanist at the University of Washington. “But in most plants, what those signals are for is an open question.”

In the case of the Venus flytrap, it’s becoming clear just how important electrical signaling can be for a plant. But much more research is needed to better understand the exact mechanisms at work. For many years, Volkov lamented, electrophysiology — the field that studies electrical properties of biological cells — largely ignored the electric aspects of plant life.

“If you open textbook on electrophysiology in the 18^th or 19^th century, they cover both electrical signals in plants and animals,” Volkov said. “But in the beginning of the 20^th century, all money for research in electrophysiology started going to medical investigation of nerves and action potentials in animal science. Many plant physiologists were using very old techniques, because the modern techniques were so expensive. But now we are much better able to measure electrical signals in plants in real time.”

Movement in the Plant Kingdom

Venus flytrap isn’t the only plant capable of rapid movement. Volkov also studies Mimosa pudica — known as the sensitive plant — whose leaves fold up instantly when touched. He’s finding that Mimosa relies on electrical signaling too. There’s also the telegraph plant, whose tiny leaflets constantly swivel to monitor the direction of light in the environment. And some of the Venus flytrap’s carnivorous cousins, the sundews, act like hungry anemones, curling their sticky sweet tentacles around whatever insect blunders into them.

These speedy plants are especially interesting to biologists — and they get our attention because we can actually observe their behavior — but researchers have recognized for decades that all plants move. Most plants simply move too slowly to see in real time.

“We see someone jerk their hands back from a flame and we understand that because we are animals,” explained the University of Washington’s Van Volkenburgh. “We don’t see plants moving or behaving because the time frame that plants use is 10 or 100 or 1000 times longer than what we’re used to.”

Some of the best understood plant movements include phototropism — shoots and leaves bending towards light — and gravitropism — roots growing in the direction of gravity, shoots away from it. These processes rely on hormones that change the rate of cellular growth in plant tissues: if one side of a root or shoot is growing faster than another, it’s going to bend. Volkov thinks electrical signaling may be involved too.

Some young plants’ flowering tops and leaves can track the sun’s movement from East to West — a phenomenon called heliotropism that allows for maximum light exposure. And climbing plants, like vines, respond to touch, changing their growth to curl around the first pole, wall, or branch they contact.

So the Venus flytrap is not really a freak of the plant kingdom. All plants move, all plants are electrical and many plants respond to touch. (Okay, maybe the eating animals thing is a little weird…) The Venus flytrap is actually a paragon of plant abilities, bringing into dramatic focus the surprising sensitivity and sophistication of the plant life all around us.