If you’re a carnivorous plant, it’s probably because you live in a barren environment, devoid of other nutrients. There are at least 600 species of carnivorous plants, some of which even eat small mammals.
Unlike other carnivores, those that grow out of the ground can’t go foraging for food. Instead, they’ve developed techniques to lure their prey to them.
One way they do this is by releasing odors that attract their prey – a hypothesis first postulated by Charles Darwin. After observing large numbers of insects caught in sundew traps, Darwin suspected that the plants must be releasing pheromones or other scents, but never tested the idea.
He was, in fact, correct – a study published in February 2016 shows for the first time that some carnivorous plants do indeed use smells to secure meals.
But here’s the problem with plants eating insects: they need insects to pollinate. When they’re ready to produce, the flower, just like other plants. Many carnivorous plants produce flowers that even appear suitable for pollinators.
So how does a carnivorous plant distinguish between a meal and a pollinator? We’re not sure, actually, but studies indicate they do have a very successful mechanism of discerning between the two. In a study of one species, less than 20% of insects caught in its trap escaped – and less than 5% of those were also found in the plant’s flowers.
Scientists have a few theories on this. One way to protect pollinators is to keep flowers away from traps. Either the flowers are physically far from the trap opening, or in the case of the pitcher plant, by ensuring that flowers bloom and die before the traps open. One-third of carnivorous plants have simply developed underwater traps, while keeping their flowers above ground.
Still, these techniques are not true for all carnivorous plants, leading to debate among botanists. Ashraf El-Sayed, chemical ecologist at the New Zealand Institute for Plant & Food Research Limited, suggests that there may be something more interesting happening here.
“We suspected that the plants might be using other cues to guide the insects,” says El-Sayed. His team is currently working on a theory that carnivorous plants may actually emit distinct odors – one for the insects it eats, and another for those the plant needs to pollinate.
“Who knows?” El-Sayed says, “Some of these chemicals might help us manage pests.”