The Pitcher Plant That Evolved to Eat Mammals

Being in front of a Nepenthes rajah for the first time has a subtle unnerving quality. The glossy, red-flecked pitchers, each open at the top as though patiently waiting, slump from the forest floor like swollen wine jugs. Some are large enough to accommodate a bottle of soda. The fluid inside, which can contain up to three liters, appears harmless until you discover that it has broken down whole frogs and occasionally small mammals.

Our thoughts of carnivorous plants have always been uncomfortable. We are conditioned to view vegetation as the part of the food chain that is eaten rather than the one that does the eating—gentle, photosynthesizing background scenery. The rule is then reversed by a plant that grows in Borneo’s mountain mists. Carnivorous plants, according to French botanist Laurence Gaume, are creatures that defy natural laws. The description doesn’t seem overly dramatic after spending an afternoon among Nepenthes specimens. It seems true.

The evolution of Nepenthes rajah is what makes it so peculiar. On the slopes of Mount Kinabalu, where nitrogen is scarce and peat is acidic, plants must find nutrients in any way they can. For a while, insects were useful. However, the supply of insects decreases above 2,200 meters, and any plant that depends only on flying meals begins to experience a shortage. Thus, the plant grew larger. Slipperier and wider. Eventually, at some point in its evolutionary history, it trapped animals with backbones by entering a region that most of its relatives had never been able to.

Here, the science is cautious and patient. After years of researching nitrogen isotopes in these species, botanist Alastair Robinson of the Royal Botanic Gardens Victoria has concluded that nitrogen capture in mammal-feeding pitchers is more than twice that of typical insect-eaters. There’s a feeling that evolution will try nearly anything if it has enough time and hunger. Some Nepenthes species even completely abandoned carnivory, using their pitchers as restrooms for tree shrews that consume lid nectar and excrete nutrient-rich excrement. A snack is given to the shrew. The plant is fertilized. It’s a strange setup, but it functions.

It’s difficult not to feel a strange admiration when you see pictures of summit rats lapping nectar in the dim moonlight of Borneo’s high forests while balancing on Nepenthes lids at night. They are not always consumed by the plant. There are instances when the relationship is only transactional. The rat slips occasionally. It’s not always easy to distinguish between mutualism and meal, and part of what draws biologists back is this ambiguity.

Little Shop of Horrors and decades of pulp fiction have shaped a cultural memory of carnivorous plants that overrides reality. Pitcher plants don’t scream or snap. They remain motionless. They have a subtle sweet scent. Until someone treads on the wrong rim, they appear decorative. Charles Darwin wrote four hundred pages about them in 1875, possibly because the drama is slow and almost contemplative.

It is genuinely unclear if Nepenthes Rajah will endure the century. Forty percent of Nepenthes species are now classified as threatened due to habitat loss, climate change, and illicit collection. Whether conservation policy can advance swiftly enough is still up for debate. The plant has spent millions of years learning how to survive in harsh environments. Now, the question is whether we will allow it to continue.