The Hunting Strategies of Carnivorous Plants
Not the blood-thirsty Audrey II from Little Shop of Horrors "“ we're talking about the very real plants that feast on insects and invertebrates. Carnivorous plants are usually found in environments with low-nutrient soil, like bogs and swamps, where they thrive on the sunshine and warm temperatures. Contrary to popular belief, carnivorous plants don't derive their energy from their prey, merely nutrients. Especially nitrogen.
The really cool thing about carnivorous plants (aside from the fact that they hunt and devour prey) is the variety of hunting mechanisms they employ. Some of these traps are more complicated than a spy-movie death apparatus. Here are some of the amazing techniques carnivorous plants use to get their fill. [Image courtesy of Playbill.com.]
Pitcher and Pitfall Plants
Have you have ever had the misfortune of finding an insect flailing around in a glass of your sugary beverage of choice? That's the basic mechanism employed by a pitcher plant. They entice prey into their rolled leaf cavities with the lure of bright pigments and nectar at the bottom of a deep, inescapable pit. The insects are intoxicated by (and then drown in) this liquid, which contains bacteria and enzymes that will eventually dissolve their carcasses. The inner tubes utilize a slippery, hairy or grooved surface to make sure even sober insects can't escape. Forget about rainwater filling the cavity and diluting the digestive juices; most pitcher plants use some sort of umbrella-like contraption to keep water out, usually a flared leaf called an operculum. [Image courtesy of PitcherPlant.org.]
In this amazing trap, the convex leaves are covered in triggers that slam shut and become concave when they sense an insect has arrived. Once shut, the lobes of the leaves are stimulated by the struggling insect and grow together to form a stomach. The glands then secrete an enzyme that digests the insect in about ten days. The ever-famous Venus Flytrap is the best example of this vicious hunting style, and there are very few other species that use this technique.
The undirected movement of the leaves in response to touch snapping is a process called thigmonasty (which sounds like a great DJ moniker to me). Just how fast is the process? Well, the Venus Flytrap can close its traps within 100 milliseconds. After digestion, the leaves re-open and can capture another victim, though it's rare for a single trap to catch more than three insects in its lifetime. Each plant has multiple traps, so it never goes hungry. [Image courtesy of MooseysCountryGarden.com.]
Here's a YouTube demonstration:
Bladder and Suction Traps
I don't particularly like the words bladder or suction, especially when paired with the word trap, but this trap type is incredible. These plants live in the water and use lots of tiny bladders to ensnare dinner. Basically, bladder traps pump ions out from their interiors and use osmosis to create a partial vacuum. If a creature triggers the trap, it is immediately sucked in, along with a bunch of extra water. The plant immediately begins to filter out the water and digest the prey, and it can hunt for more prey as it digests its current catch.
These complicated traps are exclusive to bladderwort plants, which have at least 215 species. Unlike other carnivorous plants, which exclusively eat insects, bladderworts trap water fleas, nematodes, mosquito larvae, small tadpoles and other things you don't want in your swimming water. Despite their gross-looking traps, bladderworts have beautiful flowers that are similar to orchids and snapdragons, only smaller. [Image courtesy of Carnivorous Plants Online.]
Just as the name indicates, these plants generate super-sticky glue called mucilage to trap insects. Plants cover their attractive leaves with mucilage, which resemble droplets of fresh dew or rain, and then wait for an insect to land, and fall right into their trap.
Sundew plants are a common but fascinating example of these types of plants. Sure, the name sounds warm and pleasant, but it actually refers to the glistening drops of mucilage at the tip of each tentacle that resemble drops of morning dew. Tentacles and mucilage, gross. Once an insect adheres to the plant, the tentacles very slowly move to wrap around and eventually digest the prey.
The butterwort group of carnivorous plants uses broader leaves rather than tentacles to attract prey. The huge, brightly colored leaves are completely covered in mucilage. Once an insect lands on a leaf, the plant creates more mucilage, causing the struggling insect to become encased in the sticky stuff. Other glands on the leaf secrete digestive juices, and the nutrients are absorbed by the plant leaves. [Image courtesy of Wikipedia.]
Think of these plants as the Roach Motels of carnivorous plants: insects check in, but they don't check out. The traps are easy and intriguing to enter, but very difficult to escape due to inward-pointing bristles and spiraling parts. The genlisea group of plants uses traps that have all their carnivorous parts beneath the soil. The trap is basically a pair of thin tubes joined in an inverted 'V' shape, with spiral grooves down their lengths that allow the entrance of soil-dwelling invertebrates. The grooves are lined with inward-pointing hairs that prevent the prey from escaping and instead force them into the apex of the 'V,' where they are slowly digested. [Image courtesy of CarnivorousPlants.org.]
Caroline Donnelly is an occasional contributor to mentalfloss.com. Her last story looked at 7 Famous Phrases Famous People Own.