Carnivorous Pitcher Plant Uses Rain Drops and Vibrating Lid to Capture Insects

Posted on June 13, 2012

Researchers have discovered that Nepenthes gracilis pitcher plants have another novel trapping mechanism for getting insects to plunge to their deaths. Pitcher plants are already known to have slippery surfaces on the upper rim and inner wall, which cause insects to slip and drown in the digestive fluid located at the bottom of the pitcher plant.

Researchers have now discovered that during heavy rain, the lid of Nepenthes gracilis pitchers acts like a springboard, catapulting insects that seek shelter on its underside directly into the fluid-filled pitcher.

The lead author of the paper, Dr. Ulrike Bauer from the University of Cambridge's Department of Plant Sciences, says, "It all started with the observation of a beetle seeking shelter under a N. gracilis lid during a tropical rainstorm. Instead of finding a safe - and dry - place to rest, the beetle ended up in the pitcher fluid, captured by the plant. We had observed ants crawling under the lid without difficulty many times before, so we assumed that the rain played a role, maybe causing the lid to vibrate and 'catapulting' the beetle into the trap, similar to the springboard at a swimming pool."

The scientists simulated rain drops using a hospital drip and recorded its effect on a colony of ants that was foraging on the nectar under the lid. They counted the number of ants that fell from the lid in relation to the total number of visitors. They found ants were safe before and directly after the 'rain', but when the drip was switched on about 40% of the ants got trapped. The researchers also discovered that the lower lid surface of the plant is covered with highly specialized wax crystals. This structure seems to provide just the right level of slipperiness to enable insects to easily walk on the surface under dry conditions, but lose their footing and die when the lid is hit by rain drops. The scientists also found that the lid of N. gracilis secretes larger amounts of attractive nectar than that of other pitcher plants, presumably to attract more insects to fall and die from its springboard lid mechanism.

Here are some videos of the pitcher plant's lid in action:

Dr. Bauer says, "Scientists have tried to unravel the mysteries of these plants since the days of Charles Darwin. The fact that we keep discovering new trapping mechanisms in the 21st century makes me curious what other surprises these amazing plants might still have in store!"

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