Carnivorous Venus flytraps are an exceptional American species. They make captivating houseplants, but their greenhouse popularity obscures their true scarcity. Flytraps are native to a small region of the Carolinas. There they sprout like clover in areas where scattered pine trees give way to soggy open savannas. They grow nowhere else.
Like their fellow Americans, Dionaea muscipula has an unusually meaty diet. (The typical American human eats more flesh per capita than almost anyone else on the planet.) Flytraps grow jawlike structures that snap closed around prey. They feed on invertebrates, mostly ants and spiders, which liquefy into nutrient mush within the traps.
Of the 600 species of carnivorous plants, only flytraps have this mechanism, and recent studies suggest they even can track how frequently they are touched. Yet while famous for their snapping skill, much of flytrap life is unknown.
For instance: What bug could pollinate an insect-eating plant?
Flowering plants like Venus flytraps need visitors to collect and spread pollen. “Because it's a carnivorous plant, it has this special potential for conflict that ordinary plants don't,” said Elsa Youngsteadt, an entomologist at North Carolina State University and part of a team that conducted the first study of Venus flytrap pollinators. The scientists' report was published this week in the journal American Naturalist.
Youngsteadt and her co-authors made four visits to Venus flytrap territory to collect flytrap visitors — the various bees, beetles, flies, spiders and other little things that alighted or crawled on the flowers. The scientists also gently tugged open the traps to observe what the plants were digesting. All told, Youngsteadt said Tuesday, they collected 400-odd flower visitors representing 100 species. They also tallied 200 prey animals caught by the plants. “We were surprised to see the variety of things that turned up on the flower,” she said.
They placed flower visitors on dry ice, at which point the insects “went to sleep forever,” Youngsteadt said. Back in the lab, the researchers swabbed them with cubes of gelatin, which drew pollen grains from the bugs. They then counted the grains under a microscope to determine which visitors carried the most pollen from flower to flower.
The entomologists discovered three species of repeat customer: sweat bees, as well as long-horned beetles and checkered beetles, all of which have wings. The bees, which carried about 20 pollen grains apiece, were the flytraps' most important pollinators.
What is more, the plants generally avoided turning their primary pollinators into meals. “That the identity of flytrap pollinators is mostly different from the identity of their prey is very interesting,” said John Hutchens, a biologist at Coastal Carolina University in South Carolina, who was not a part of this research.
Youngsteadt and her co-authors do not have an exact answer for why prey and pollinator do not overlap. They are now examining the differences between the plant's trap and flower. The color of the trap can vary from red to shades of green, while the flower is always white, and it is possible the structures produce specific scents.
There is another obvious difference between in the two features: altitude. About six inches of plant separates the flower from the deadly parts down below. “Most of our flower visitors were arriving on the wing,” Youngsteadt said. Most prey come on foot.
What pollinates a flytrap is an interesting ecological question, and it may be a vital environmental one. “Maintaining natural habitats with all of their species and interactions intact is essential if we hope to have wild populations of Venus' flytraps in the future,” Hutchens said.
Before this research, Youngsteadt had never seen a flytrap in the wild. In centuries past, wildfires regularly swept through their habitat, and the plants flourished in those cleared-out ecosystems. Human fire suppression has upended that pattern and made life tougher for the flytraps. In addition, other vegetation has out-competed the plants in many places.
Poaching, too, is a problem, despite North Carolina law making it a felony to harvest wild plants. In January 2015, four men were the first to be arrested for poaching Venus flytraps; They had collected nearly a thousand specimens, estimated to be about 3 percent of the wild flytrap population. In 2016, ecologists proposed the plant be included on the federal endangered species list. Their petition remains active.