Slippery trap

Science World, March 31, 2008 by Cathy Tran

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Most plants get all the nutrients they need from sunlight, air, and soil. But not carnivorous pitcher plants; these meat-eaters capture small animals that fall into the plants' liquid-filled, bowl-shape leaves. Then, the plant digests them. New research shows the slippery traps may be even trickier than that.

On dry days, ants and other insects can trot easily across the lip of some pitcher plants and carry away the plants' sugary nectar. On wet days, however, ridges on the bowl's outer edge trap rain droplets and dew, says Walter Federle, a zoologist at the University of Cambridge in England. This watery film reduces the friction that bugs need to grip the plant. Without this resistance to movement, these unlucky insects lose their footing and fall to their doom.

Scientists used to think that the rim of the pitcher plant was harmless based on only observing it during days of dry weather, says Federle. Now they know better.

RECONNAISSANCE: An ant gathering nectar from a pitcher plant on a dry day may think the plant is safe, When it brings more ants back, they may all fall to their deaths if it's wet out.