Carnivorous plants tend to grow in places where the soil is thin or lacking in nutrients like bogs and rocky areas, so these plants must get some of their nutrients by trapping and digesting animals, especially insects. More than 600 species and subspecies of carnivorous plants have been identified, although some are now extinct. The Venus’s-flytrap is probably the most famous.
Catching a Meal
Just like other plants that need to attract other creatures to help with things like pollination, carnivorous plants use different strategies to attract their prey. Some are sweetly scented, others are brightly colored, still others have parts that are sticky or slippery or designed in a way that makes it hard for prey to escape. Once they have attracted their dinner, carnivorous plants use five basic trapping strategies:
- Pitfall traps (like pitcher plants), in which the prey falls into a rolled leaf that contains a pool of digestive enzymes and/or bacteria at the bottom;
- Flypaper traps, that use a sticky glue substance to hold onto unsuspecting insects;
- Snap traps (like the Venus’s-flytrap), where the leaves actually snap shut to create a plant prison;
- Bladder traps, which use a bladder to suck in aquatic creatures; and
- Lobster-pot traps, which use inward-pointing hairs to force prey towards the digestive enzymes.
The Venus’s-flytrap has long been an object of fascination (it even stars in a movie!). How does the plant move? Does it have muscles? Venus’s-flytraps aren’t the only type of carnivorous plant that moves, but they are the most commonly known. When something touches the trigger hairs on the edges of the leaves, the cells on the inside wall of the trap transfer water to the outside walls, so the inside essentially goes limp. This makes the leaf snap closed. Another way carnivorous plants move can be observed in sundew plants, which have a long flypaper trap. Once the prey gets stuck on the gluey tentacles, the tentacles embrace the creature by growing faster on the outside than the inside. And they can do this really fast. One species of sundew can bend 180º in only a minute or so!
The Digestion Question
So once they catch their prey, how do these plants digest the meal? Most carnivorous plants make their own digestive enzymes. Still others depend on bacteria to produce these enzymes; the bacteria cause the captured prey to rot and the plant absorbs the nutrients. Still other plants rely on both their own enzymes and additional enzymes generated by bacteria. Yet another method is even more unappetizing. Some carnivorous plants use bugs and insects as helpers. For example, on carnivorous sundews, assassin bugs crawl around and eat the insects that have been captured. Then these bugs poop and the feces provide dinner for the plant! Yuck!
Most carnivorous plants eat flying, foraging, or crawling insects. Those that live in or around water capture very small aquatic prey like mosquito larvae and tiny fish. On rare occasions, some tropical carnivorous plants have even been reported to capture frogs, or even rats and birds (although these creatures were probably sick or already near death)! But don’t worry, these plants pose no danger to humans, even if you fell asleep in a whole bed of them.