Asian pitcher plant eats bugs with a little help from rain

An insect-eating pitcher plant found in Southeast Asia uses the power of rain drops to flick ants crawling on the underside of its waxy lid into a pitcher, where they can be digested.

British scientists with the University of Cambridge report on the findings, which were published Wednesday in the journal PLoS ONE.

'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' —Ulrike Bauer, University of Cambridge

The research focused on a specific type of pitcher plant, the Nepenthes gracilis, common in Malaysia, Singapore and western Indonesia.

Ulrike Bauer, the study's lead author, found that under normal conditions, ants were able to cling upside-down to a unique wax crystal surface of the lid, which is suspended above a trap containing digestive enzymes.

But once rain hit the surface of the lid, unlucky insects sheltered beneath it were knocked off by the impact and fall to their doom.

Unique method of capturing insects

While researchers have noted before that the inner walls and rims of most pitcher plants become more slippery after rain, causing more insects to drown in the fluids below, the Nepenthes gracilis demonstrated a unique method of capturing insects for food.

"It all started with the observation of a beetle seeking shelter under a N. gracilis lid during a tropical rainstorm," Bauer said in a release.

"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 researchers tested their hypothesis with simulated rain from a hospital drip and found 40 per cent of the ants foraging for nectar under the lid became victims when the drip was switched on.

The authors concluded that the Nepenthes gracilis possesses a unique mechanism than other pitcher plants.

"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," Bauer said.