In a carnivorous plant, researchers have discovered an unusual way to catch insects

(ORDO NEWS) — The unusual strategies of carnivorous plants for catching live prey have long captured the imagination of scientists.

But even in this strange group of plants, in which food capture mechanisms have evolved several times independently, some oddities stand out.

For example, the showy pitcher plant Nepenthes gracilis, native to Southeast Asia, can use the energy of falling rain to lie in wait for animals in ambush.

A new study published in the journal Biology Letters demonstrates how the structure of the plant’s pitcher component, itself a modified leaf, makes an unusual strategy work.

“This is the only time we know of a plant actually using [external energy] for a specific purpose,” said study co-author Ulrike Bauer, an evolutionary biologist at the University of Bristol in England.

But how does this rain trap work?

The pitcher of this species has a rigid horizontal lid with an open underside that releases nectar, luring insects to land on it.

When a raindrop hits the top of the lid, the lid comes down and throws any unsuspecting visitor into the digestive juices below.

Bauer and study lead author Ann-Christine Lentz used high-resolution X-ray images to analyze the cross sections of the jars when the lid is up, down and in neutral.

Their results revealed a structural weakness, which the researchers called a torsion spring, in the mouth of a jug: when a raindrop hits the lid, the weak spot flexes and causes the lid to slide down like a diving board.

The weak spot causes the pitcher’s body to flex and lean back in a certain, consistent fashion, so the lid lifts up without bouncing too much – unlike the chaotic wobble of a regular leaf in the rain.

The researchers also found that the closely related pitcher plant Nepenthes rafflesiana did not have this mechanism.

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