Plants that eat insects do so to obtain nutrients, not energy, which they obtain through photosynthesis, the same as other plants. Capturing and digesting insect prey is thought to be the way these plants evolved to survive in soils that lack nitrogen. Botanists tell us that these amazing plants capture their prey in five different ways.
The pitfall trap is also called the pitcher trap. The plant uses bright colors, flowers or an attractive scent to lure its insect prey into a pit, or pitcher. The bottom of the pitcher is filled with fluid produced by the plant or by rainwater. The insect hits the fluid, gets its wings wet and eventually drowns. It sinks to the bottom of the fluid, where it decomposes or is digested by plant enzymes.
Some pitfall traps have sticky or slimy walls that prevent the insect from escaping. Some pitchers have lids over their mouths to keep out rain and attract bugs with sugary nectar on the underside. An overindulging insect, sated on the nectar and bloated, easily plops into the lethal pit.
Some carnivorous plants have stalks with glands that produce a gummy mucous. The leaves on top of these stalks are sticky. A bug lands on a sticky leaf and can't escape. Some plants digest the trapped insects with enzymes. Others leave the job to symbiotic insects that live on the plant. Some plants have slimy tentacles that fold over the trapped prey, clasping it so the enzymes can digest it.
Lobster Pot (Eel Traps)
These traps are similar to the pitfall traps. In a lobster pot, the death chamber has sheer walls that prevent the prey from escaping. The plant uses colorful flowers or a sweet scent to lure a foraging insect into a wide entrance. The prey continues through a small, narrow hole from which there is no escape.
Some plants capture insects with a combination of pitfall trap and lobster pot; having been lured through a small entrance, the prey finds itself in a large chamber with sheer walls from which there is no escape.
This is the method of capturing prey used by the famous venus flytrap, found in the southeastern United States, and by the waterwheel plant, found in Europe, Asia and Australia. These plants have leaves with special hairs on the interior. When a foraging insect lands on the hairs, the leaves snap shut. The trapped insect attempts to escape. As it does, it stimulates the hairs, and the plant tightens its grip, smothering the insect.
One carnivorous plant, the bladderwart, captures prey with a kind of suction cup. This flexible suction cup, a kind of pouch or bladder, is underwater. At rest, the bladder bulges, filled with water. The plant uses special glands to expel the fluid, collapsing the bladder. The collapsed, puckered bladder has small hairs on the entrance. When a foraging insect lands on the bladder, the disturbed hairs cause the bladder to open, then water rushes in, sweeping the insect with it.