Carnivorous plants can survive in poor soils by adding insects to their diet and have developed traps to do this. But what happens when prey is difficult to catch? Adam Cross and colleagues examined how some plants employ mammals to hunt and deliver prey to them. Their chemical analysis, published in Annals of Botany, shows that when insects are scarce, this is an effective strategy for survival.

Carnivorous plants are a group of plants that have evolved to capture and digest their prey to supplement their nutrient requirements. Nepenthes is the largest family of these plants, occurring throughout the Palaeotropics. They can be found as vines, possibly on trees, or else as low shrubs. They get their common name, Pitcher Plant, from a characteristic leaf structure in the form of a pitcher, which evolved primarily to attract, capture and digest prey.

The pitchers have an overhanging lid and a cylindrical peristome or specialised lip around the pitcher’s mouth. Inside the pitcher, the walls contain glandular zones and wax crystals, making it difficult for prey to grip, causing them to fall into the pitcher. The pitcher also contains an enzyme cocktail that helps break down and absorb nutrients from the prey.

Not only do Nepenthes species inhabit poor soils, but many live in ultramafic soils, soils with a high concentration of toxic elements like nickel or cobalt. These soils are found around Mount Kinabalu and Mount Tambuyukon, both located in Borneo, and both particularly rich in Nepenthes species. It’s at the high elevations of these mountains where botanists have spotted what appear to be morphological adaptations to capture and consume mammalian waste. Effectively the pitchers act as toilet bowls for small animals.