Researchers reveal how an insectivorous plant uses rain energy to power its traps

Scientists at the University of Bristol have discovered the deadly effect of a carnivorous plant.

In Borneo’s steamy jungle, plants have developed countless tricks to help them survive and outperform their neighbors. The slender pitcher plant, Nepenthes gracilis, is one of the most ingenious: Its elaborate cup-shaped leaves are outfitted with a canopy-like hanging lid that turns into a deadly springboard for ants when hit by a falling raindrop.

The findings, published today in Biology Lettersreveal for the first time how the deadly spring works.

The team was surprised to find that the spring does not flex in the lid itself or in the narrow constriction between the cup and lid, but rather sits way down the back of the tubular cup wall. The eccentric location at the back of the tube has two effects.

First, it makes the spring directional and therefore the lid moves down easily, but not up. When a raindrop falls, the lid is quickly sped down, shooting any insects sitting at the bottom into the liquid-filled trap below. On the way up, the increased resistance of the spring slows the lid down so it stops moving sooner and the trap is quickly ready to catch again.

Second, the eccentric spring prevents the lid from twisting or wobbling, maximizing the transfer of impact energy in downward motion.

Lead author Anne-Kristin Lenz of Bristol’s School of Biological Sciences explained: “When you look at the shape of the jug, you would assume that the deformation occurs at the smallest cross section, which is the transition point from lid to jug tube, but in fact it is it also deforms further down the back of the throwing tube.

“Pitcher plant traps are lightweight, yet sturdy. Nepenthes gracilis uses small changes in the shape of the trap to transfer impact energy with amazing efficiency. We can learn from these plants how to geometrically optimize structures, which can help save material and weight.” , while with a functional spring. The springboard’s catch mechanism could even provide inspiration for designing new mechanical devices for harvesting energy from rain or hail.”

This clever use of geometry makes Nepenthes gracilis the only known plant to use an external energy source to achieve extremely fast movements – completely free of metabolic costs.