This Plant Calls to Bats So They Will Poop in it

Specially shaped reflectors bounce back the squeaks of echolocating bats

bat and pitcher plant
A graphical abstract from the paper shows the bat approaching its pitcher plant partner. Schöner et al./Current Biology 2015. Additional images courtesy of C.C. Lee and M.D. Tuttle.

Most people and animals are quite happy to get rid of their waste, whether junk mail, garbage, or urine. But plants aren’t as discriminating — they enjoy nitrogen-rich leavings (as any tomato plant tucked into a rich compost will attest). This has led to some interesting partnerships between plants and animals. Take, for instance, tropical bats and the pitcher plants who sing to them.

Pitcher plants don’t have voices of their own, but Nepenthes hemsleyana, some particularly large pitchers, do have a way of reflecting a bat’s sonar pings back at it, reports Ed Yong for National Geographic

Like many other pitcher plants, N. hemsleyana grows in soils that are relatively nutrient poor. To make up for the deficit, most pitchers secrete a viscous fluid that collects in the elongated vase-like structures that give them their name. Bugs unlucky enough to fall in this liquid drown and break down in the digestive enzymes the plant releases. But N. hemsleyana has its own, unique style of gathering nutrients. 

Instead of capturing bugs, they provide shelter for roosting Hardwicke’s woolly bats. As the bats hang out inside the plants during the day, they pay rent with nitrogen-rich droppings, researchers found in 2011. Now the same team has uncovered how the bats find the pitchers amid a the very lush tropical forests in Borneo where it grows.

Inspired by a flower that reflects the calls of echolocating bats in South America, the team used a robotic bat head to test the pitcher plants. Yong writes:

It has a central loudspeaker and two microphones that look like a bat’s ears. He used it to “ensonify” the pitchers with ultrasonic calls from various directions, and measure the strength of the echoes.

The team found that the back wall of N. hemsleyana—the bit that connects its lid to its main chamber—is unusually wide, elongated, and curved. It’s like a parabolic dish. It strongly reflects incoming ultrasound in the direction it came from, and over a large area. 

After modifying some plants’ parabolic dishes, the researchers saw that bats preferred unmodified reflectors that would return their calls loud and strong. The team published their findings in Current Biology

N. hemsleyana isn’t the only pitcher to woo small mammals in order to get their poop. Another species of pitchers in Borneo uses sugary secretions to lure tree shrews and rats to hang out, take some sips and hopefully leave some feces. This kind of relationship is far more mutually beneficial than that between other pitcher plants and their insect prey — at least, most of the time: The second species has been known to digest the occasional shrew or rat that slips and falls into its belly.

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