We may not have to dodge them en route to the nearest green tunnel, but nearly 700 species of carnivorous plants exist on our planet. Some, like the infamous Venus fly trap, use volatile compounds to draw in their insect prey. But others prefer a sneakier solution: meet the Cape sundew (Drosera capensis), a master of disguise whose beauty is a deadly ruse.
The leaves of this carnivorous plant are covered with bright red tentacles that secrete a delicious-looking gelatinous goo from their tips. The glistening liquid fools winged passersby into flying close, mistaking the droplets for food. And while it isn’t sweet, the secretion is sticky – very sticky. Once landed, an insect has little chance of escape.
The fluid (called mucilage) contains a weak acid and enzymes that digest the soft parts of its hapless prey. A small meal, like an ant or termite is easily broken down, but when necessary, the leaves will also roll inwards to suffocate any strugglers.
So plants actually have a sense of touch? Yes. And in some cases, they’re far more sensitive than we are. A human can just minimally detect a 0.002 milligram thread being drawn across their arm. The leaves of the sundew, on the other hand, will respond to a thread that weighs just 0.0008 milligrams. That’s 775 times lighter than a single human hair.
The tentacles are so sensitive, in fact, that they not only can detect an ensnared insect, but also differentiate between prey and a non-edible item. Studies have shown that sundews do not, for example, respond to rain drops.
Now, this doesn’t mean that plants feel in the same way we do. Plants, of course, don’t have brains or central nervous systems, but their cells can “communicate” using chemical cues, and react accordingly. This response to stimuli is known as thigmotropism, and it’s the same process that allows plants like peas and vines to climb. As the plant’s tendrils make contact with the surface, the cells on the opposite side will elongate, while the cells on the touched side will shrink. This causes the plant to continuously bend around the object it’s touching.
Another great example of a thigmotropic plant is Mimosa pudica (also known as the “touch-me-not plant”). When prodded, the Mimosa folds into a protective state by reducing fluid pressure to the edge veins on one side of each leaf.
Plants don’t need brains any more than we need leaves – we should all be thanking our lucky stars for that, really. We’d be pretty useless against a horde of actively thinking carnivorous plants. (Cough, cough, “feed me,” cough). Not to mention, realistic piranha plants are terrifying.