Question corner | What powers the traps of Slender Pitcher plant to catch insects?

Scientists at the University of Bristol have uncovered the deadly workings of a carnivorous plant — Slender Pitcher plant ( Nepenthes gracilis). The Slender Pitcher plant in the steaming jungles of Borneo has developed one of the most ingenious tricks to help them survive and outcompete their neighbours. Its elaborate cup-shaped leaves are equipped with a canopy-like hanging lid that turns into a deadly springboard for ants when it is hit by a falling rain drop. The findings ( Biology Letters) reveal for the first time how the lethal spring works.

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

First, it makes the spring direction-dependent and as a result, the lid moves easily down, but not up. When a rain drop hits, the lid is accelerated quickly downwards, flicking any insects sitting on its underside into the fluid-filled trap below. On the way up though, the increased resistance of the spring slows the lid down, so that it stops moving sooner and the trap is quickly ready to capture again, says a release.

Second, the off-centre spring prevents the lid from twisting or wobbling, thereby maximising the transmission of impact energy into downward movement.

This clever use of geometry makes  Nepenthes gracilis the only known plant to exploit an external energy source to achieve extremely fast movement — entirely free of metabolic costs.

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