Some plants get so hungry they eat flies, spiders, and even small frogs. What's more amazing is that these plants occur naturally (in special environments) in every state. In fact, they're found on every continent except Antarctica.
You've probably seen a Venus' flytrap. It's often sold in museum gift stores, department stores, and even supermarkets. A small plant, it grows 6 to 8 inches tall in a container. At the end of its numerous elongated stalks are specially modified leaves that act like traps. Inside each trap is a lining of tiny trigger hairs. When an insect lands on them, the trap snaps shut. Over the course of a week or so, the plant dines on its catch.
The Venus' flytrap is just one of more than 500 species of carnivorous (meat-eating) plants, says Barry Meyers-Rice. He's the editor of the International Carnivorous Plant Society's newsletter. Note: Despite any science-fiction stories you might have read, no carnivorous plant poses any danger to humans.
Dr. Meyers-Rice says a plant is carnivorous (or insectivorous, "insect eating"), only if it does all four of the following: "attract, kill, digest, and absorb" some form of prey. Prey includes a number of nectar-loving insects including flies, butterflies, and moths. Carnivorous plants look and act like other green plants - well, most of the time.
All green plants make sugars through a process called photosynthesis. Plants use the sugars to make food and nectar. What makes "meat-eating" plants different is their bug-catching leaves. They need insects for one reason: nitrogen. Nitrogen is a nutrient that they can't obtain any other way. Why?
Almost all green plants on our planet get nitrogen from the soil. Carnivorous plants can't. They live in places where nutrients are hard or almost impossible to extract from the soil because of its acidity. So they've come to rely on getting nitrogen from insects and small animals. In fact, nutrient-rich soil is poisonous to carnivorous plants. Never fertilize them! But don't worry, either, if they never seem to catch any insects. They can survive, but they'll grow very slowly.
Most carnivorous plants live in bogs and wetlands. To be called a bog, an area must have sphagnum moss and water of a specific acidity. Bogs are usually fed by rainwater only. No in-flowing streams or underground springs bring in outside nutrients.
Many carnivorous plants grow alongside streams, or in other areas that are consistently moist. If the ground does dry out, some plant species become dormant - they hibernate, in effect. Or, the parent plant may produce seeds and die. When weather conditions are favorable again, the seeds grow into new plants.
Jerry Hinkley is a biology professor at the College of Lake County in Grayslake, Ill. He takes his science classes on field trips every year to see carnivorous plants. They go to a "quaking bog" just outside Volo, Ill. When someone steps on this sphagnum moss-carpeted bog, each footstep makes the ground bounce up and down, or "quake" slightly.
Hinkley has found small clumps of pitcher plants in Volo Bog. The pitcher plants are a "dazzling thing to see," he says.
Pitcher plants (plant family, Sarraceniaceae) have an exotic urn or pitcher-shaped appearance, hence their name. Instead of traps that snap shut, like the Venus' flytrap, pitcher plants use a passive approach to detain their prey.
Insects like the plant's flowerlike appearance and the scented nectar held at the base of the plant. Once inside the pitcher, insects either travel downward or fall in. Special digestive enzymes take over. Meyers-Rice points out that these digestive enzymes are extremely weak. They are more like saliva than stomach acid. In any case, he adds, "They are entirely harmless to people."
One species, Sarracenia purpurea, is especially widespread. The purple pitcher plant lives as far north as British Columbia in Canada, along the eastern portions of North America, and in southern sections of Florida and west to Mississippi.
Winged pitchers, sticky 'dew'
Greg Harmison, a horticulturist at Mercer Arboretum in Humble, Texas, describes the carnivorous plants in his area. The winged pitcher plant, (S. alata), can grow to be three feet tall. Its pitcher-shaped leaves are yellowish-green with a reddish lid-shaped top. It can live in both moist areas and sandy savannahs. In warmer climates, enterprising gardeners create special boglike sites. Imagine raising these plants in your backyard! Pitcher plants can also be grown indoors, in terrariums.
Another "dime-size" carnivorous plant is the sundew (Drosera). Its leaves look like a whorl of flattened spoons. On the "spoon" portion are tiny, sticky glands that look like hairs. In most cases they are bright red and glisten as if covered with dew. When prey lands on it, it gets stuck.
Visitors to Big Thicket National Preserve near Beaumont, Texas, can see these plants up close. Sundews also grow in the Pacific Northwest, northern California, and across eastern North America.
Of all the carnivorous plants in Mr. Harmison's area, perhaps the smallest is the bladderwort (Utricularia). They are from 1/3 inch to 3 inches tall. Bladderworts float in slow-moving fresh water and form large clumps.
They set a unique trap to catch their prey. It's like "a bladder that's not inflated," Harmison says. Trigger hairs are located on the trap door. When these triggers are touched, the bladder inflates. This causes it to suck in water and anything else that's nearby. This happens within 1/30 to 1/100 of a second. Once inside the bladder, the prey is digested.
Later, the water is pumped out and the trap is reset for another meal. This may take a couple of days.
Maybe it's just starting a garden
Not all bladderworts may be carnivorous, says Doug Darnowski. He's a biology professor at Washington College in Chestertown, Md. Some bladderworts, he notes, "might just have 'gardens' in their traps." A recent study suggests that bladderworts "aren't really trapping - they're cultivating," he says. Think of them as having a "little terrarium inside their trap." Nothing like homegrown food.
Carnivorous plants have learned to adapt to survive. But they aren't the only ones making the best of a bad situation. Plant expert Meyers-Rice says some creatures have figured out how to take advantage of the meat eaters. It seems some pitcher plants have creatures living inside their nectar-filled pitchers.
One Southeast Asian pitcher (Nepenthes ampullaria) may have mosquito larvae, spiders, and ants making a home inside it. There is even a frog (genus Philautus) that lays its eggs in the nectar. As long as the creatures are alive (even in egg form), the nectar's digestive enzymes won't harm them. The enzymes can only start to break down prey after cracks appear in a creature's outer covering.
Some enterprising spiders stop by to pull out prey that has fallen inside a pitcher plant. What an easy meal! And this may actually help the plants, too. Tiny insects and spiders are easy to digest, but bigger prey may not break down properly. If undigested, the carcasses may putrefy and destroy the leaf. Diving ants come to the rescue by seizing and removing overly large prey. Just think of it as housekeeping service.
*** How to raise your own Venus' flytrap
Outside of arboretum collections, carnivorous plants are hard to find - even for experts who know where to look. Instead of tramping into sensitive wetlands, try a more ecological approach: Order plants from a catalog. (See list at end.) Try a Venus' flytrap as a start.
You will need:
Plastic planter with a drainage hole at the bottom. A 4-inch pot will hold one Venus' flytrap. Use larger pots for more plants.
Peat moss. (Do not use sphagnum moss.)
Horticultural sand. (Do not substitute. Some sand contains plant-toxic salt.)
Distilled water or water purified by reverse osmosis (check the label). Both are available at most supermarkets. Do not use tap water. Do not use bottled drinking water unless it's 'low sodium.'
Deep saucer to place under planter.
One or more Venus' flytraps. (See source list.)
Mix soil: half peat moss, half horticultural sand.
Fill pot three-quarters full of soil. Place your plant or plants in the soil. Make sure the roots are covered. Water thoroughly.
Fill bottom saucer with an inch of water. Place planter in saucer. Water in the saucer will provide needed humidity as it evaporates.
Set planted container and saucer in a location that gets from 3 to 6 hours of direct sun every day during the plant's growing season (April to September).
Never fertilize carnivorous plants. You can feed them insects if they don't catch any, but don't worry if they don't. They will still grow, but slowly.
In autumn, move the planter to a chilly window (about 45 to 55 degrees F.) to let the plants go dormant. In April, return the plant to a sunny window.
Keep the soil moist, but not soggy. You shouldn't see standing water.
You can raise other kinds of carnivorous plants, but not all species like the same growing conditions as the flytrap. You may need several planting environments.
Happy, healthy Venus' flytraps can live for several decades.
The following website lists carnivorous-plant dealers. They are reputable and do not forage plants from the wild.
Two sources on that list include:
Botanique 387 Pitcher Plant Lane Stanardsville, VA 22973
7020 Trenton-Healdsburg Rd. Forestville, CA 95436
Phone: (707) 838-1630
For more information on carnivorous plants (and photos) go to the nonprofit International Carnivorous Plant Society (ICPS) website: www.carnivorousplants.org/ index.html
Barry Meyers-Rice, contacted for this story, is an editor for the ICPS newsletter. In cooperation with the society, he has put together a list of answers to frequently asked questions about carnivorous plants: www.sarracenia.com/ faq.html
(c) Copyright 2001. The Christian Science Monitor