This Carnivorous Plant Has a Rain-Powered Trap

This Carnivorous Plant Has a Rain-Powered Trap

A biological “spring” helps a pitcher plant fling insects to their doom

Credit: Paul Starosta/Getty Images
The unique strategies of carnivorous plants for grabbing live prey have been a long-cherished fascination. But even within this strange group, in which food-trapping mechanisms have evolved multiple times independently, some oddities stand out. For example, the visually striking pitcher plant Nepenthes gracilis, native to Southeast Asia, can harness falling rain’s energy to ambush animals. A new study in Biology Letters demonstrates how the structure of the plant’s pitcher component, itself a modified leaf, makes the unusual strategy work.

” This is the only case where a plant actually uses [external energy] to accomplish a purpose,” says Ulrike Bauer (a co-author of the study). Ulrike Bauer is an evolutionary biologist and biomechanist from the University of Bristol, England. But how does this rain-powered trap work?

This species’ pitcher has an opaque underside and a rigid horizontal lid. It secretes nectar which lures insects to it. The lid’s top is triggered by a raindrop. It jolts down and throws any uninitiated visitor into the digestive juices below. Anne-Kristin Lenz (also at Bristol) used high-resolution scans to examine the cross sections of pitchers when the lid was raised, lowered, or in neutral. The researchers discovered a structural weakness in the pitcher’s neck, which they called a torsional Spring. When a raindrop hits the lid it buckles and causes the lid to slide downwards, similar to a diving board. The pitcher’s body is affected by the weak point. It causes the lid to bend and snap back in a consistent manner. This prevents the lid from bouncing too far, unlike a typical leaf’s chaotic oscillations caused by rain. The researchers also found that a closely related pitcher plant, Nepenthes rafflesiana, lacked this mechanism.

” This is a really good study that is comparing 2 species and getting back at this diversity among them,” Tanya Renner, Pennsylvania State University entomologist, said. Although the rain-trap technique so far seems unique to N. gracilis, Renner hopes future work will examine more of the extensive diversity seen in carnivorous plants. She says that she would like to see more .”


This article was originally published with the title “Science in Images” in Scientific American 327, 5, 26-27 (November 2022)

doi: 10. 1038/scientificamerican1122-26b


    Darren Incorvaia is a writer and comedian based in Chicago. Follow him on Twitter @MegaDarren

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