Bats in Borneo roost in carnivorous pitcher plants

By Ella Davies
Earth News reporter

Bats in Borneo have been found roosting in carnivorous pitcher plants.

A new study reveals that the plants benefit from nutrients in the bats' droppings.

This unusual living arrangement is apparently beneficial for the bats too as they can shelter unseen inside the plants' pitchers.

Although tree shrews have also been observed using pitcher plants as toilets, this is the first time mammals have been found living inside them.

Nepenthes carnivorous pitcher plants grow in nutrient-poor soil and rely on trapping insects to acquire enough nitrogen for growth.

Found in the peat swamps and heath forest of Borneo, N. rafflesiana elongata are remarkable for their long aerial pitchers.

However, research has previously suggested that N. r. elongata catch up to seven times less insects than other pitcher plants in Borneo.

The pitcher plant benefits from attracting the bat because the bats defecate into the pitcher, using it as a toilet Dr Ulmar Grafe

In a new study, published in the journal Biology Letters, scientists found that the unique subspecies had a extraordinary relationship with mammals.

Dr Ulmar Grafe and his team investigated how the plants supplemented their nitrogen intake and were surprised to find woolly bats inside the pitchers.

"It was totally unexpected to find bats roosting in the pitchers consistently," says Dr Grafe.

The small Hardwicke's woolly bats (Kerivoula hardwickii) were found roosting above the digestive fluids in the plants' pitchers.

Rather than consuming the whole bat for extra nitrogen, Dr Grafe found that the plants gained from the bats' waste.

The darker shadow in this pitcher is a roosting bat

"The pitcher plant benefits from attracting the bat because the bats defecate into the pitcher, using it as a toilet if you will," he explains.

This unusual arrangement also has advantages for the bat according to Dr Grafe.

"The bat benefits from having a secure roosting place that is also free of blood-sucking ectoparasites that often accumulate in bat roosts," he tells the BBC.

Last year, researchers observed tree shrews using another type of pitcher plant (Nepenthes rajah) as a toilet and likewise found that the plant benefited from nitrogen in the deposits.

However, this is the first time mammals have been found living inside carnivorous plants.

Dr Grafe points to these findings as evidence that biodiversity is key to protecting the planet's wildlife.

"This is one of many animal-plant mutualisms... that highlights the fact that extinction or removal of a single species within an ecosystem will impact many other species," he says.