Pollinators are usually safe from a Venus flytrap

Out of the hundreds of species of carnivorous plants found across the planet, none attract quite as much fascination as the Venus flytrap. The plants are native to just a small section of North Carolina and South Carolina, but these tiny plants can now be found around the world. They’re a favorite among gardeners, who grow them in homes and greenhouses.

Scientists, too, have long been intrigued by the plants and have extensively studied the famous trap. But far less is known about the flower that blooms on a stalk 15 to 35 centimeters above — including what pollinates that flower.
“The rest of the plant is so incredibly cool that most folks don’t get past looking at the active trap leaves,” says Clyde Sorenson, an entomologist at North Carolina State University in Raleigh. Plus, notes Sorenson’s NCSU colleague Elsa Youngsteadt, an insect ecologist, because flytraps are native to just a small part of North and South Carolina, field studies can be difficult. And most people who raise flytraps cut off the flowers so the plant can put more energy into making traps.

Sorenson and Youngsteadt realized that the mystery of flytrap pollination was sitting almost literally in their backyard. So they and their colleagues set out to solve it. They collected flytrap flower visitors and prey from three sites in Pender County, North Carolina, on four days in May and June 2016, being careful not to damage the plants.

“This is one of the prettiest places where you could work,” Youngsteadt says. Venus flytraps are habitat specialists, found only in certain spots of longleaf pine savannas in the Carolinas. “They need plenty of sunlight but like their feet to be wet,” says Sorenson. In May and June, the spots of savanna where the flytraps grow are “just delightful,” he says. And other carnivorous plants can be found there, too, including pitcher plants and sundews.
The researchers brought their finds back to the lab for identification. They also cataloged what kind of pollen was on flower visitors, and how much.
Nearly 100 species of arthropods visited the flowers, the team reports February 5 in American Naturalist. “The diversity of visitors on those flowers was surprising,” says Youngsteadt. However, only three species — a sweat bee and two beetles — appeared to be the most important, as they were either the most frequent visitors or carriers of the most pollen.
The study also found little overlap between pollinators and prey. Only 13 species were found both in a trap and on a flower, and of the nine potential pollinators in that group, none were found in high numbers.

For a carnivorous plant, “you don’t want to eat your pollinators,” Sorenson says. Flytraps appear to be doing a good job at that.

There are three ways that a plant can keep those groups separate, the researchers note. Flowers and traps could exist at different times of the year. However, that’s not the case with Venus flytraps. The plants produce the two structures at separate times, but traps stick around and are active during plant flowering.

Another possibility is the spatial separation of the two structures. Pollinators tend to be fliers while prey were more often crawling arthropods, such as spiders and ants. This matches up with the high flowers and low traps. But the researchers would like to do some experiments that manipulate the heights of the structures to see just how much that separation matters, Youngsteadt says.

The third option is that different scents or colors produced by flowers and traps might lure in different species to each structure. That’s another area for future study, Youngsteadt says. While attraction to scent and color are well documented for traps, little is now known about those factors for the flowers.

Venus flytraps are considered vulnerable to extinction, threatened by humans, Sorenson notes. The plant’s habitat is being destroyed as the population of the Carolinas grows. What is left of the habitat is being degraded as fires are suppressed (fires help clear vegetation and keep sunlight shining on the flytraps). And people steal flytraps from the wild by the thousands.

While research into their pollinators won’t help with any of those threats, it could aid in future conservation efforts. “Anything we can do to better understand how this plant reproduces will be of use down the road,” Sorenson says.

But what really excites the scientists is that they discovered something new so close to home. “One of the most thrilling parts of all this,” Sorenson says, “is that this plant has been known to science for [so long], everyone knows it, but there’s still a whole lot of things to discover.”