Most carnivorous plants eat insects to maintain their nutrient supply, but this species from Borneo has other ideas. Its pitcher is extremely roomy, oddly shaped, and contains very little of the necessary "digestive juices" to consume insects. And when researchers checked inside the "bellies" of hundreds of these pitcher plants, they did not see very many insect caracasses-- instead, they found little woolly bats sleeping happily! What is going on here?
The plant, Nepenthes hemsleyana, presents a rare and intriguing example of mutualism. Its unusually shaped leaves reflect the sonar of calling bats, effectively "talking" like another bat, to lure in its chiropteran tenants*. Instead of trapping and eating insects, Nepenthes acts as landlord to sleeping bats, happily eating their nitrogen-rich guano as payment.
Interestingly, when the researchers built up or trimmed back the leaf structures that reflected bat calls, the bats were much quicker to approach the larger (more reflective plants), but upon arrival were wary of the strangely augmented plants. This is strong evidence for the acoustic purpose of these leaves, but also demonstrates that the bats are making reasoned assessments of potential pant motels. If it looks a little "off," like the plants changed by researchers, the bats-- like a father who peels away from a seedy motel 6 despite a huge VACANCY sign -- resume their search for more standard accommodation.
One cannot help but think of these pitcher plants as the more peaceful cousins of their bloodthirsty insectivorous relatives, like bonobos versus chimps. Perhaps they are evidence that the energy spent in predation - searching, hunting, capturing - will always be greater than the energy required for mutualistic relationships (only collaborative searching required)? Or perhaps they were the surviving members of the Triffids, demonstrating that -- in the end-- collaboration beats predation every time.
*This plant is not the only one to evolve bat-attracting structures; another species of flower (pollinated by bat) uses its blooms as sonar dishes to help bats identify the flower amidst a sea of greenery.
Imagine a bat flying through the jungle of Borneo. It calls out to find a place to spend the night. And a plant calls back. The plant in question is Nepenthes hemsleyana—a flesh-eating plant that’s terrible at eating flesh. It’s a pitcher plant and like all its kin, its leaves are shaped like upright vases. They’re meant to be traps. Insects should investigate them, tumble off the slippery rim, and drown in the pool of liquid within the pitcher. ... But N.hemsleyana has very big pitchers that are oddly short of fluid and that don’t release any obvious insect attractants. And when Ulmar Grafe from the University of Brunei Darussalam looked inside them, he saw seven times fewer insects than in other pitchers.