Flesh-eating killers: assassin or ally? Scientists get the dirt on the relationship between predatory plants and their victims.

The world is a dangerous place--especially for insects. Beyond the reach of plastic flyswatters, these six-legged critters still need to watch where they land. Hunting for a place to rest its weary wings, an unsuspecting fly may settle upon what looks like a harmless leaf. But if its resting spot happens to be the lobe (leaf) of a Venus flytrap--snap!--it may end up as the plant's next meal. That's because Venus flytraps are carnivorous (meat eating) and snack on organisms like flies, grasshoppers, or even large lizards that venture too close. "We don't know exactly why every carnivorous plant eats other organisms," says botanist Barry Rice, director of conservation for the International Carnivorous Plant Society. "But they are obviously deficient in some nutrients."

POWER UP

Just like other plants, meat-eating greens make their own food. They use the sun's energy to turn carbon dioxide and water into glucose (sugar) during photosynthesis. Additionally, plants normally absorb other nutrients--like the elements nitrogen and phosphorous--from the soil through their roots.

But carnivorous planks live in nutrient-poor areas, such as wetlands called bogs. So instead of relying on the soil, carnivorous plants get nutrients from the flesh of organisms crawling and flying around them. "They have a competitive advantage over noncarnivorous plants," says Rice. "So you'll usually see many different species of carnivorous plants in these [nutrient-poor] areas."

SNEAK ATTACK

Without legs to chase down prey, carnivorous plants need a stealthier tactic to catch their meals: traps. Take the Venus flytrap, chock-full of moving parts. When an insect brushes against the inside of the plant's clam-shaped leaf, the active trap snaps shut. And the victim? Clamped between jail-cell prongs, or spines, it will be a nutritious meal for the plant.

Even fish aren't sale from active traps. When prey happen to float by a carnivorous bladderwort growing in a pond, a tiny door on the plant's underwater sac quickly opens, sucking in water--and tiny swimming organisms--in one hundredth of a second. "It's the fastest motion known in the plait world," adds Rice.

Other carnivorous plants, like pitcher plants, have passive traps. They leave the chore of catching their next meal to luck. An ant attracted to a pitcher-plant's honey-like nectar may accidentally fall into the plant's deep, cone-shaped bowl. Insects that fall in can't climb the slippery walls to escape. Instead, they drown in fluid at the bottom--a mixture of rainwater and digestive liquids secreted by the plant.

HAPPY MEAL

After a carnivorous plant has captured its prey, it dissolves the meal to absorb nutrients. Most meat-eating plants produce enzymes (proteins that aid in body functions) that liquefy the insect's soft tissues. Then cells on the surface of the plant's leaves absorb nutrients from the insect soup. It can take up to two weeks for a plant to completely digest its captured prey.

Parts of the victim dissolve at different rates often leading to strange sights. "The last thing that remains of frogs in a pitcher plant is the thick skin from their hands," says Rice. "If you peek into the pitcher, all you'll find are some little frog gloves!"

HAZARDOUS HOME

You'd think the danger of ending up as lunch would keep insects from making their homes anywhere near predatory plants. But some invertebrates (organisms without backbones) dare to live inside the plants.

Why take the risk? Scientists have discovered: It's not just a plant-eat-bug world out there. New research suggests that some of these meat eaters have developed symbiotic (mutually beneficial) relationships with their prey. "They aren't just these vampires that lurk on the edge of the plant world," explains Rice. "They actually have a friendly relationship with some insects."

Take the Nepenthes bicalcarata, a species of pitcher plant: The pitchers are attached to the plant's leaves by a fat, hollow tendril--the perfect home for a small ant colony. "The ants chew a hole through the stem to access this hollow chamber," says biologist Robert Gibson, a member of the International Carnivorous Plant Society. The tendril provides protection from predators and rain which can flood ant homes on the ground. Bonus: The ants feast on the sweet nectar along the pitcher's rim.

But the ants aren't the only ones who benefit from this unlikely partnership. Every once in a while, one of the scurrying ants slips into the pitcher giving the plant a tasty treat. Since there are so many ants in the colony, the ants find that the value of a cozy home far outweighs the occasional loss of a colony member.

FOOD PROCESSORS

Scientists have also discovered that some insects help carnivorous plants better absorb nutrients. How? The insects eat a meal, then deposit "leftovers" for the plants.

Some insects--adapted to life around carnivorous plants--can walk on a plant's gummy leaves without getting stuck. These clever creatures steal food captured by the plant. "There are bugs that make their homes on the leaves of sundews and feed on trapped invertebrates," explains Gibson.

Sound like a raw deal for the pickpocketed plant? Think again. Having its prey stolen doesn't mean the plant is out of a meal. After the scavenger insect digests the prey, it excretes waste onto the plant's leaves or near its roots. The plant absorbs nutrients from the waste.

Traditionally scientists have classified a plant as carnivorous if it attracts, captures, kills, digests, and absorbs prey on its own. Now researchers know some carnivorous plants need the help of other organisms to digest prey. "It's becoming clear the plants are not strictly carnivorous or noncarnivorous--they use blended approaches," explains Rice. So what do you call a carnivorous plant? Rice says, "Scientists are still figuring that out."

It's Your Choice

1 Carnivorous plants eat insects and other organisms because

A. the plants do not photosynthesize.

B. insects taste good.

C. they protect the plant from predators.

D. the plants are deficient in

nutrients.

2 Which of the following best describes the symbiotic relationship between ants and Nepenthes bicalcarata?

A. Ants protect the plant from predators in exchange for food.

B. Insects that would prey on ants are eaten by Nepenthes bicalcarata.

C. The plant provides shelter and food to ants in exchange for the occasional meal when an ant falls into the pitcher.

D. The ants help Nepenthes bicalcarata digest prey,

3 According to the article, why do some carnivorous plants produce enzymes?

A. To feed insects.

B. To liquefy prey's tissues so the plant can absorb nutrients.

C. To attract insects.

D. To provide food for organisms.

4 If an insect steals their prey, some carnivorous plants will get nutrients from

A. nearby plants.

B. the excreted waste of the scavenger insect.

C. nectar.

D. sunlight.

Did You Know?

* Many carnivorous plant species are in danger of extinction. Why? Many of the wetlands they 'thrive in have been destroyed to build shopping malls, homes, and farms. "We have removed about 95 percent of carnivorous plant habitats in the U.S.," says Barry Rice of the International Carnivorous Plant Society.

* If a Venus flytrap shuts a leaf but does not capture prey, the lobe reopens within hours. But if it does catch a prey, it takes five to 12 days before the leaf reopens. Usually, a trap can close and reopen about half a dozen times before it becomes inactive. Then the leaf acts like a normal plant leaf: It photosynthesizes to provide the plant with sugar before falling off a few months later.

Flesh-Eating Plants

1. Just like noncarnivorous plants, carnivorous plants produce food through photosynthesis.

2. Carnivorous plants live in nutrient-poor areas, such as in wetlands called bogs. Instead of relying only on the soil for nutrients, carnivorous plants also get nutrients from the flesh of organisms crawling and flying around them.

3. Carnivorous plants have either active traps or passive traps.

4. A carnivorous plant dissolves its prey to absorb nutrients. Most meat-eating plants produce enzymes that liquefy the insect's soft tissues. Then cells on the surface of the plant's leaves absorb nutrients from the insect soup.

5. A symbiotic relationship is one that is mutually beneficial. For example, the Nepenthes bicalcarata pitchers are attached to the plant's leaves by a hollow tendril. Ants chew a hole through the stem to access this hollow chamber, which provides protection from predators and rain. The sweet nectar along the pitcher's rim also provides food for the ants. But when ants slip into tam pitcher, the plant gets fed.

Directions: Answer the following questions in complete sentences.

1. How are carnivorous plants like noncarnivorous plants?

2. Where are carnivorous plants usually found? How does their meat-eating ability help then; in this environment?

3. Carnivorous plants possess two different types of traps. What are they?

4. How does a carnivorous plant get nourishment from its prey?

5. What is a symbiotic relationship? Use the relationship between the Nepenthes bicalcarata and an ant colony as an example.

Bonus: Write a short story about the day in the life of a carnivorous plant--from the plant's point of view.

It's Your Choice, p. 13

1. d 2. c 3. b 4. b

Resources

Barry Rice's Web site has great photographs and facts about carnivorous plants: www.sarracenia.com/faq.html

For tips on growing your own carnivorous plants, visit the California Carnivores store: www.californiacarnivores.com/

The Savage Garden by Peter D'Amato, Ten Speed Press, 1998.

Carnivorous Plants by Adrian Slack, Trans-Atlantic Publications, 2000.