Matthew Fertakos | May 4, 2026

Carnivorous plants have evolved a unique way of obtaining necessary nutrients for growth and survival in environments where they are lacking: by trapping and digesting insects. One carnivorous plant you may be familiar with is the Venus Fly Trap (Dionaea muscipula) which uses a snapping mechanism to trap flying prey for digestion. Pitcher plants are another type of carnivorous plant which produce large jug-shaped modified leaves filled with an acidic digestive liquid and topped by a lid. Insects are attracted to the pitcher’s scent, visual UV reflection patterns, or nectar produced by the plant, and then fall in due to the pitcher’s slippery upper surface (known as the peristome [1]). One genus of pitcher plant is especially diverse: Nepenthes, consisting of approximately 120 species found in the tropics of Southeast Asia [2]. However, not all pitcher plants focus exclusively on insect prey, and three species of Nepenthes have a particularly unique relationship with shrews that allows for nutrient acquisition in a way you probably have never considered! 

Three species of pitcher plant – Nepenthes lowii, Nepenthes rajah, and Nepenthes macrophylla (Fig.1) grow at high elevations in the mountains of the island of Borneo [2] where there are few insects [3] making nutrient acquisition through carnivory especially difficult. 

Figure. 1 – (a) Nepenthes lowii (b) Nepenthes rajah ( c) Nepenthes macrophylla (Sources: Rudolphous, Weft, and Hirosi via Wikimedia Commons). 

Mountain Tree Shews (Tupaia montana) are present at the same altitudes, but here their diets of large fleshy fruits and seeds are not as abundant as the lower altitudes of their range. From these two situations a unique relationship not seen anywhere else on Earth has developed: shrew toilets (Fig. 2).

Figure 2. A mountain tree shrew (Tupaia montana) feeding on the nectar from a Nepenthes rajah pitcher plant. (Source)

These 3 pitcher plant species produce nectar on the undersides of their lids which attract and habitually feed the tree shrews in the high mountains. While feeding, the shrews are perfectly positioned over the open pitcher of the plant so a well-timed defecation can deposit the nitrogen and phosphorus the plant needs to survive [2]. This relationship is an example of a mutualism, where both parties benefit from an interaction. The shrews get nectar and the plant receives vital nutrients. Check out a short video showing this interaction below.

It is the unique geometry of their pitchers which allows these plants to serve as perfect shrew toilets: they have large orifices with concave lids oriented at near right angles [4] and reduced peristomes to prevent the shrews from slipping [5]. In fact, this interaction is so specialized that the distance between the nectar source and the front of the pitcher in these species exactly matches the body size of the tree shrew that feeds on it [4]. This suggests that these three species of Nepenthes have evolved specifically to take advantage of this unique nutrient source. When this relationship was first forming, pitcher plants which could better attract shrews and capture their defecations had a fitness advantage over those that could not, slowly shaping the anatomy of plants in the population to what we see today.

The relationship between mountain tree shrews and pitcher plants shows how evolution can lead to really cool relationships between plants and animals. Remember: If you’re a shrew needing to poo, but can’t find a loo, the mountainous regions of Borneo might be the place for you!

References 

[1] Mithöfer, A. “Carnivorous pitcher plants: Insights in an old topic.” Phytochemistry 72: 1678-1682 (2011). https://doi.org/10.1016/j.phytochem.2010.11.024.

[2] Clarke, C., J. A. Moran, and L. Chin. “Mutualism Between Tree Shrews and Pitcher Plants: Perspectives and Avenues for Future Research.” Plant Signaling & Behavior 5: 1187–1189 (2010). https://doi.org/10.4161/psb.5.10.12807.

[3] Collins, N. M. “The Distribution of Soil Macrofauna on the West Ridge of Gunung (Mount) Mulu, Sarawak.” Oecologia 44: 263–275 (1980). https://doi.org/10.1007/BF00572689.

[4] Chin, L., J. A. Moran, and C. Clarke. “Trap Geometry in Three Giant Montane Pitcher Plant Species from Borneo is a Function of Tree Shrew Body Size.” New Phytologist 186: 461–470 (2010). https://doi.org/10.1111/j.1469-8137.2009.03166.x.

[5] Clarke, C. M., U. Bauer, C. C. Lee, A. A. Tuen, K. Rembold, and J. A. Moran. “Tree Shrew Lavatories: A Novel Nitrogen Sequestration Strategy in a Tropical Pitcher Plant.” Biology Letters 5: 632–635 (2009). https://doi.org/10.1098/rsbl.2009.0311.

[6] Greenwood, M. G., C. Clarke, G. Kerth, and T. U. Grafe. “A Unique Resource Mutualism between the Giant Bornean Pitcher Plant, Nepenthes rajah, and Members of a Small Mammal Community.” PLOS ONE 6: e21114 (2011). https://doi.org/10.1371/journal.pone.0021114.