When it rains, sometimes it's better to just get wet—especially when staying dry could mean being digested alive. That's the hard lesson for insects hiding from showers underneath the lid of the slender pitcher plant (Nepenthes gracilis). During a downpour, the carnivorous plants, native to the Sunda region of Southeast Asia, rely on heavy raindrops crashing on top of their lids to help catapult shelter-seeking insects into their tube-shaped, fluid-filled leaves, researchers report online today in PLoS ONE. Like a diver jumping on a swimming pool springboard, the pounding raindrops create vibrations throughout the lid that launch insects off its underside and directly into an awaiting acid bath . Previously, scientists thought the lid simply prevented rainwater from diluting the leaf's digestive pool. But upon further investigation, researchers realized the structure's prey-capturing function. The underside of the lid has evolved to be covered with wax crystals which interfere with the adhesive pads found on an insect's feet. The wax crystal layer is only semislippery, so when nothing is hitting the lid, an insect has little problem crawling upside down on it, and will often do so to collect nectar. But with sudden impacts like rainfall, an insect easily loses its footing on the surface—literally falling victim to the pitcher's fatal trap.
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