致命诱惑:食虫植物

A hungry fly darts2 through the pines in North Carolina. Drawn by what seems like the scent of nectar3 from a flowerlike patch of scarlet on the ground, the fly lands on the fleshy pad of a red leaf. It takes a sip of the sweet liquid oozing4 from the leaf, brushing a leg against one tiny hair on its surface, then another. Suddenly the fly’s world has walls around it. The two sides of the leaf are closing against each other, spines5 along its edges firmly joining together like the teeth of a jaw trap. As the fly struggles to escape, the trap squeezes shut. Now, instead of offering sweet nectar, the leaf releases enzymes6 that eat away at the fly’s innards7, gradually turning them into goo8. The fly has suffered the ultimate indignity for an animal: It has been killed by a plant!

The swampy9 pine savanna10 within a 90-mile radius11 of Wilmington, North Carolina, is the one place on the planet where Venus flytraps are native. It is also home to a number of other species of carnivorous plants, less famous and more widespread but no less bizarre12. You can find pitcher plants13 with leaves like champagne flutes14, in which insects(and sometimes larger animals)lose themselves and die. Sundews15 envelop16 their victims in an embrace of sticky tentacles17. In ponds and streams grow bladderworts18, which slurp19 up their prey like underwater vacuum cleaners20.

Darwin’s Studies

There is something wonderfully unsettling about a plant that feasts on animals. The topsy-turvy21 ways of carnivorous plants greatly interested Charles Darwin. In 1860, soon after he encountered his first carnivorous plant, the sundew Drosera, the author of Origin of Species wrote,“I care more about Drosera than the origin of all the species in the world.” He spent months running experiments on the plants. He dropped flies on their leaves and watched them slowly fold their sticky tentacles over their prey. He excited them with bits of raw meat and egg yolk22. He marveled23 how the weight of just a human hair was enough to cause a response. “It appears to me that hardly any more remarkable fact than this has been observed in the vegetable kingdom,” he wrote. Yet sundews ignored water drops, even those falling from a great height. To react to the false alarm of a rain shower, he reasoned, would obviously be a“great evil”to the plant. This was no accident. This was adaptation.

Darwin expanded his studies from sundews to other species, eventually recording his observations and experiments in 1875 in a book, Insectivorous Plants. He marveled at the exquisite quickness and power of the Venus flytrap, a plant he called “one of the most wonderful in the world.” He showed that when a leaf snapped shut, it formed itself into “a temporary cup or stomach,” releasing enzymes that could dissolve the prey. He noted that a leaf took more than a week to reopen after closing and reasoned that the interlocking spines along the margin of the leaf allowed small insects to escape, saving the plant the expense of digesting an insufficient meal. Darwin likened the hair-trigger speed of the Venus trap’s movement—it snaps shut in about a tenth of a second—to the muscle contraction of animals. But plants don’t have muscles and nerves. So how could they react like animals?