Flesh-eating plant doubles as bat-cave

By Ed Yong | January 25, 2011 7:00 pm

The world’s worst flesh-eating plant lives in the jungles of Borneo. It’s called elongata and it’s one of several strains of Raffles’ pitcher plant. Like its relatives, it has distinctive pitcher-shaped leaves that can lure insects into a watery grave. But unlike other strains, elongata is strangely incompetent at catching insects. Instead, it lures bats into its pitchers, and lives off their poo.

Pitcher plants grow in soils that lack the vital nitrogen that plants depend on. The pitchers make up for this shortfall by harvesting nitrogen from the flesh of animals. Their pitchers are traps, baited with nectar, enticing colours, or tempting smells. If an insect approaches and falls in, it is doomed. It can’t clamber up the slippery side of the pitcher, and it soon drowns in the pool of liquid at the bottom. This fluid contains a suite of enzymes that breaks down the plant’s prey, releasing its valuable cache of nitrogen and other nutrients.

Elongata looks much like other pitcher plants, except for its giant traps. They’re around four times larger than those of its relatives, they don’t contain much fluid, and they don’t emit any noticeable smell. At such a size, you’d expect the pitchers to be swimming in insects. But when Ulmar Grafe from the University of Brunei Darussalam looked inside the giant pitchers, he found six to seven times fewer insects than in other pitchers. Instead, he found small bats.

Grafe spent a year trekking through Bornean swampland to inspect a group of 400 elongata pitchers. In that time, he found 32 Hardwicke’s woolly bats, nestled inside. By fitting them with radio-trackers, Grafe found that these bats are exclusive tenants. They nest nowhere else besides these meat-eating plants.

Their green apartments are roomy affairs, adapted to suit their hosts. There’s not a lot of fluid inside, so the bats don’t inadvertently drown. There’s a thickened “girdle” half-way up, which gives them purchase against the slippery sides. And there’s enough space for two – on two occasions, Grafe found youngsters snuggling with their parents.

In the pitchers, the bats get shelter from predators and the elements. But what does the plant get in return for providing a living bat-cave? In a word: faeces. The bats defecate into the pitchers, providing the plant with at least a third of its nitrogen, packaged in neat dollops.

This is just the latest in a long line of alliances between pitchers plants and animals. Three species turn their pitchers into latrines for tree-shrews. They produce nutritious nectar that the tree-shrews can only reach if they position their backsides over the mouth of the pitcher. Tree-shrews often mark valuable resources with poo, and when they do so into the pitcher, they provide it with fertiliser. One of these – the king pitcher – has the largest pitchers in the world. They need to be, to double as suitable toilets.

That’s just the mammals. The leafy traps can actually house entire communities of creatures and some of these residents are found nowhere else on the planet. Small invertebrates swim within the fluid, including the larvae of various mosquitoes, midges and flies. The black-spotted sticky frog uses the liquid as a nursery for its tadpoles. By eating the animals that die within the pitcher, these residents speed up the release of nutrients. They may be tenants, but they double as part of the plant’s digestive system.

And some predators have taken to raiding the pitchers for food. A type of carpenter ant called Camponotus schmitzi nests solely in the tendrils of the pitchers, and it risks life and limb by actually diving into the fluid to grab drowned prey. A red crab spider can do the same; it spends its life in the pitchers, picking off drowned insects and hauling itself to safety with lifelines of silk.  Strangest of all, a small red land crab also raids the pitchers for food. They might be death-traps, but the pitcher plants can also be havens for life.

Reference: Grafe, Schoner, Kerth, Junaidi & Schoner. 2011. A novel resource–service mutualism between bats and pitcher plants. Biology Letters http://dx.doi.org/10.1098/rsbl.2010.1141

More on plant-animal alliances:

CATEGORIZED UNDER: Animals, Bats, Mammals, Plants

Comments (7)

  1. Pitcher plants must be the coolest plants out there!

  2. Nathan Myers

    Wow. Just … Good one, Ed.

    Speaking of bats, do we have any reliable reports of robins eating them? Other passerines do.

  3. hat_eater

    “I sheltered a bat for a year and I got sh*t for that”
    attachments: [elongata.png]

  4. Joe Marfice

    OMG! OMG! OMG! I love you SOOO much for this article!

    I used to grow all sorts of insectivorous plants, and never knew that Nepenthes species did anything but. OMG!

    You know why this is such a great adaptation? I’ll tell you! Insectivorous plants grow in mineral-poor environs. In fact, in one test, a breeder showed that the reason that fertilizers kill venus flytraps (which are perfectly happy growing on nothing but sphagnum moss and water) is that they allow fungus to grow, because the fertilizers make the root culture nutritious enough for the fungus to start.

    The bat guano is incredibly mineral-rich – it’s still mined as a fertilizer component. But it’s far from an all-around fertilizer; most fungi & plants couldn’t survive the nitrogen-heavy content. Now, drop a *little* of that guano into the salivations of N. elongata, and add that to the plant juices, and you suddenly have a healthy pitcher plant! In the bowl of the pitcher, however, you have a very inhospitable, “over-mineraled” goo… so the pitcher is actually safer from fungal attack than if it filled its “mouth” with dead insects! (I bet…)

  5. Eleanor

    I’m waiting for the discovery of the predatory, mimetic version of this which springs shut in daylight and eats the bat.

    (I am very charmed by the picture of the tree shrew on its pitcher plant potty)

  6. Amazing! A nice apartment with a toilet, what more can a bat wish? Just a pedantic correction, the name of the plant is Nepenthes rafflesiana var. elongata.


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