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CCU Atheneum: Venus flytrap
Venus flytrap

CCU scientists take on Darwin's flytrap theory

by Mona Prufer
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Two notable facts: Darwin got it wrong. And the Venus flytrap (Dionaea muscipula) does not commonly trap flies.

In 1875, in a scientific book called Insectivorous Plants, the English naturalist Charles Darwin, best known for his theory of evolution by natural selection, wrote in great wonderment about “a plant [that] should secrete, when properly excited, a fluid containing an acid and ferment, closely analogous to the digestive fluid of an animal.”

It was the Venus flytrap, and Darwin went on to hypothesize that the plant only captured larger prey, allowing smaller insects to escape its hairy, springy trap during the second of hesitation as trap closes.

Coastal Carolina University biologists Jim Luken, a plant ecologist, and John Hutchens, an aquatic ecologist, have disproved Darwin’s hypothesis. Their research has just been published in Botany (Hutchens and Luken, 2009; 87:1007-1010) and the February issue of Smithsonian magazine.

“This [Darwin’s] elegant idea for optimal trap function has persisted through the years, but few scientists have tested its validity by assessing and measuring prey items found inside the traps of wild plants,” write Hutchens and Luken. Darwin’s 19th century research, after all, was conducted with very limited access to wild plants.

“We examined how plant size and surrounding vegetation influence prey capture success and prey composition,” writes Hutchens on his Web site.

After sampling hundreds of Venus flytraps at nearby Lewis Ocean Bay Heritage Preserve, Luken and Hutchens discovered that the rare plant, endemic to a 100-mile stretch of South and North Carolina, actually eats small insects, too, without discrimination. In fact, nearly anything that wanders into its gaping maw is fair game. Ants and spiders were mostly found in the traps, some beetles, millipedes and centipedes, maybe an occasional fly, but not a plethora of them.

The research showed little support for Charles Darwin’s hypothesis in 1875 that Venus flytraps select for large prey, they say.

Luken, the self-described “plant guy,” and Hutchens, the “bug guy,” were originally struck by the lack of good data about the Venus flytrap. “Though flytraps can be found around the world, in greenhouses and on windowsills, they are only found naturally here in the Carolinas,” says Luken, who has studied the popular insect-eating species since moving to the area in 2001.

Their research was conducted in 2006 over nine months, through three seasons, fall, winter and spring (summer was too dry). Aided by then-undergraduates Sunni Stewart and Scott Tomko, the scientists observed the plants and harvested closed traps to bring back to the lab. The enclosed exoskeletons of dead prey were studied under the microscope with careful measurement of length to determine the actual size of the insects.

According to the study, prey composition of 580 traps contained spiders (31 percent), ants (26 percent) and beetles (12 percent). “We found very few flies,” says Hutchens.

Next the pair plans to study the flytraps in their natural habitat, capturing the insects they would normally consume, as compared to flytraps that are introduced to an environment and fed supplemental diets.

But, as Luken points out, the larger issue is the declining number of Venus flytraps due to development, drought and poachers.

Still, there are tens of thousands of the tiny plants that range from fingernail size to teacup proportion in the 100-mile stretch of habitat of northern South Carolina and southern North Carolina. But you might be lucky enough to find some closer by.

“If you want to see some, there are flytraps on the CCU campus, over by the swimming pool,” says Luken. “I think Coleen Lohr (retired biology professor) planted them many years ago.”

Luken also admits to throwing out the tiny black flytrap seed at the entrance of his subdivision, Carolina Lakes. They’re thriving, he says, and he and Hutchens laugh about him becoming the “Jimmy Appleseed” of the carnivorous little plant.

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