Pitcher plants harness rain energy to capture insects

A study published in the journal Biology Letters has shed some light on the predatory mechanisms of the Slender Pitcher Plant, Nepenthes gracilis. This plant is native to the lush jungles of Borneo. The leaves of pitcher plants have a beautiful but deadly design; they are shaped like a cup with a hanging lid. When rain hits the lid, it closes, trapping any hapless insects on the underside and flicking them into the pitcher, where the digestive juices consume them. 

The Slender Pitcher Plant is the only known plant to use an external energy source (rain) to execute such a fast movement without having to sustain any energy costs itself. Until now, botanists were not sure how the lid works. Researchers at the University of Bristol were surprised to discover that the spring is located at the back of the tubular pitcher wall, rather than in the lid itself.

“If you look at the pitcher shape you would assume that the deformation happens at the smallest cross section, which is the transition point from lid to pitcher tube, but in fact it also deforms further down at the back of the pitcher tube,” explained study lead author Anne-Kristin Lenz.

There are two advantages to this location. First, it makes the spring direction-dependent. This means that when rain falls on the lid, it can quickly close and spring insects into the trap below. However, as the lid moves up, there is more resistance, meaning the trap is ready to claim its next victim.

Secondly, the off-center position of the spring prevents the lid from twisting or tilting, making it more stable and ensuring more energy can be devoted to the critical closing action. Lenz believes this design could inspire alternative energy engineers.

“Pitcher plant traps are lightweight, but sturdy. Nepenthes gracilis uses small changes in the trap shape to transmit impact energy with astounding efficiency,” said Lenz.

“We can learn from these plants how to optimize structures geometrically, which could help to save material and weight, while still having a functional spring. The springboard trapping mechanism might even provide inspiration for designing new mechanical devices for harvesting energy from rain or hail.”

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By Erin Moody , Earth.com Staff Writer