Plants that are large enough to catch and eat people or other large prey only exist in fantasy novels and our imagination, but their smaller, real-life cousins are just as fascinating. Whether it’s the thought of underdog plants turning the tables or our fascination with something that seems out of the natural order, the idea of plants eating animals is strangely compelling.
For a long time, people refused to believe that plants could deliberately eat animals. It wasn’t until Darwin (yes, that Darwin) published a book on the subject that attitudes began to change. Today we know that carnivorous plants come in a variety of sizes and forms, and they eat insects, and not, say, antelope.
If you have a mental image of carnivorous plants, more likely than not it’s of the Venus flytrap (Dionaea muscipula), with its strange spiky traps armed and waiting to surprise unsuspecting insects. Flytraps are interesting not only because they catch and eat insects, but because of the speed with which they move when they trap their prey. While we now know that many plants can move in response to stimuli, the movement that flytraps use is unique.
Flytraps are far from the only type of carnivorous plants. There are four other mechanisms that carnivorous plants use to trap prey.
Several different species of carnivorous plants use a pitfall type trap to catch prey. Among them, is the aptly-named ‘pitcher plant’ which has leaves that form a container or pitcher. This receptacle fills with water, catching insects in the same way a glass of water will if you leave it outside. Some pitcher plants also have a ‘lid’ that keeps out excess rainfall and prevents their insect snacks from washing away. Pitcher plants will also use pheromones and scent attractants to lure insects and even small animals to their watery deaths.
Not all pitcher plants rely on insects. Some of the larger species, such as Nepenthes rajah, also trap mice and small lizards, and in 2009, scientists discovered the five-foot tall Nepenthes attenboroughii, a pitcher plant that’s definitely large enough to make me think twice about what it might be eating. Yet another truly bizarre species, Nepenthes lowii, has essentially toilet-trained the neighbouring tree shrews, feeding them nectar in exchange for their droppings.
A third type of carnivorous plant uses sticky substances to trap its prey. The most familiar of these is likely the sundew (Drosera spp.), which secretes a glue-like substance at the end of long hairs. Insects that touch the hairs are engulfed by the plant and digested.
Scientists are learning new things about carnivorous plants all the time. In 2019, it was discovered that the western false asphodel (Triantha occidentalis), secretes a sticky substance from its stem to trap insects.
A less well known type of carnivorous plant uses a ‘lobster-pot’ style of trap to catch its prey. In these plants, insects enter a one-way passage where directional hairs prevent them from exiting and escaping digestion.
Finally, are the bladderworts (Utricularia spp.), which use a vacuum to trap insects, usually, but not always, in water. Using a hair trigger, these plants suck their prey into a bladder where the water is expelled and the insect is digested. I once found this plant in a local wetland and was extremely excited when I identified it.
So, why do some plants eat insects? It’s likely that carnivorous plants evolved their predatory ways as a means of gaining valuable nutrients. These mechanisms have evolved separately in different species, in what is referred to as convergent evolution. As many carnivorous plants live in less hospitable habitats such as peat bogs, catching their own food gives them an edge when it comes to survival.
Our world would definitely be poorer without the weirdness of carnivorous plants, but I think we can all be grateful that the monster-sized versions only exist in our imaginations.