How an insect-eating plant uses energy from rain to power its traps

Scientists from the University of Bristol have discovered the deadly workings of a carnivorous plant.

In the steaming jungles of Borneo, plants have evolved countless tricks to help them survive and outperform their neighbors. The slender pitcher plant, Nepenthes gracilisis among the most ingenious: its elaborate cup-shaped leaves are fitted with a canopy-like hanging lid that turns into a deadly springboard for ants when struck by a falling raindrop.

The conclusions, published in Biology Lettersreveal for the first time how the lethal source works.

The team was surprised to find that, rather than bending into the lid itself or the narrow constriction between the pitcher cup and the lid, the spring is located far to the rear of the tubular wall of the pitcher. The off-center location at the back of the tube has two effects.

First, it makes the spring direction-dependent, and therefore the lid moves easily down, but not up. When a raindrop hits, the lid is quickly accelerated downward, sending any insects sitting on its underside back into the liquid-filled trap below. Going up however, the increased resistance of the spring slows the lid down, so it stops moving sooner and the trap is quickly ready to capture again.

Second, the off-center spring prevents the cover from twisting or wobbling, maximizing the transmission of impact energy in the downward motion.

Lead author Anne-Kristin Lenz from Bristol’s School of Biological Sciences explained: “If you look at the shape of the pitcher, you would assume that the deformation occurs at the smallest cross-section, which is the transition point of the lid to the pitcher tube, but in fact it also deforms further down the back of the pitcher tube.The pitcher plant traps are lightweight, yet sturdy. Nepenthes gracilis uses small changes in the shape of the trap to transmit impact energy with amazing efficiency. We can learn from these factories how to geometrically optimize structures, which could help save material and weight, while having a functional spring. The springboard’s trapping mechanism could even inspire the design of new mechanical devices to harvest energy from rain or hail.

This clever use of geometry makes N. gracilis the only plant known to harness an external energy source to achieve extremely rapid movement at no metabolic cost.

– This press release was originally published on the University of Bristol website