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Meet the Venus Flytrap

By Gwen Bruno (gwen21February 7, 2012
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If your knowledge of carnivorous plants derives entirely from the satirical comedy “Little Shop of Horrors,” in which a blood-thirsty plant threatens to take over the world, you might think species like the Venus flytrap are dangerous. The truth is, carnivorous plants have far more to fear from humans than the other way round.

Gardening picture

Of course, carnivorous plants present no danger to people, and in fact many species are threatened with extinction due to human encroachment on their swampy habitats. Because the bogs in which they reside are poor sources of necessary nitrogen, carnivorous plants have evolved the ability to supplement their diets with nutrients gleaned from insects or other small creatures. These “meat-eating” plants are found on every continent except Antarctica, and can be categorized by their trapping mechanism. Some, like the pitcher plant, trap insects by luring them into a "pit." Other kinds of carnivorous plants, like the sundew or butterwort, use a kind of natural fly paper to prevent insects from escaping. Still others, including the Venus flytrap, are spring traps, with leaves that clamp shut on their prey.

Dionaea muscipula
The most familiar and easily recognizable of all the carnivorous plants is the Venus flytrap, or Dionaea muscipula. Its most unusual feature is its hinged leaves, each forming a “mouth” edged with deliciously menacing-looking “teeth.” The Venus flytrap grows naturally in only one place in the world -- the coastal plains of North and South Carolina. Botanist Charles Darwin, who first classified and described the Venus flytrap, was fascinated by the species and declared it “one of the most wonderful plants in the world.”

Special Leaves
The leaves of the Venus flytrap lure insects both by their reddish coloring and by producing a sweet nectar. A Venus flytrap plant usually contains about six insect "traps," each of which measures some three inches across. The trap is formed by the two lobes ImageImageof a leaf, which fit together like a clamshell. The inside of each lobe contains three trigger hairs (see close-up at right).

Once an insect bumps into two of the hairs, water rushes out of the inner cells of the leaf, triggering the lobes to close and encase the insect. The whole movement takes place in under one second's time. This spring-trap action demands a great deal of the plant. Each leaf can close only three or four times before it turns black and falls off. The Venus flytrap has evolved in such a way that it carefully conserves precious energy. The plant’s nectar is produced far enough away from the trigger hairs that tiny insects unworthy of a meal can land without setting the leaf in motion. Also, two hairs must be touched successively, or one hair touched twice within 20 seconds, before the closing mechanism is triggered. This helps prevent the leaf from closing unnecessarily.

How can a plant -- with no muscles, tendons, or nervous system -- move quickly enough to trap an insect? The Venus flytrap’s quick reflexes remain something of a mystery to scientists, according to the Botanical Society of America. Some theorize that the fluid pressure stimulating the leaf’s closure might be generated by an actual electrical current.

DigestionImage
Once the leaf is triggered to close, the plant again conserves energy by shutting only part way, with the cilia or spines overlapping so that they look like the bars of a prison cell. At this point, a very small insect can still escape from between the spines. If no insect remains in the trap, the leaf reopens within 24 hours. If the leaf has caught suitable prey, however, it closes so tightly around its victim that the insect’s outline can be seen from the outside of the leaf (see photo at right). Once the leaf is tightly shut, the plant produces digestive fluids that absorb nutrients from the insect’s body. According to Larry Mellichamp and Paula Gross, authors of “Bizarre Botanicals,” the enzymatic juices sometimes ooze from the leaf’s edges, making the plant appear to drool!  After several days, digestion is complete and the leaf reopens. Nothing remains of the insect but the exoskeleton, which either blows away in the wind or is washed off by rain.

The Venus flytrap's primary prey is large ants, but it will capture whatever is available, including flies, beetles, slugs, spiders and even tiny frogs. The leaves' air-tight seal not only holds the prey in, but keeps bacteria out. If the leaves should close on food that is too big to be completely sealed, bacteria growth on the dead insect can cause the plant to rot and die.

Care of the Venus Flytrap

As long as you provide it with the right culture, you can grow a Venus flytrap in a boggy area outdoors, or indoors as a houseplant. Success with the plant depends on how closely the environment you provide mimics its natural habitat. Venus flytraps require full sun, constant moisture and an acidic environment.

DO
DON'T
• feed with a fly or small slug twice monthly during the plant's active growing season

use a mixture of sphagnum moss and sand rather than regular potting soil

• expect the plant to enter a period of dormancy in the winter months

• don't drain the plant's energy by triggering the closing mechanism unnecessarily

• don’t add fertilizer to the soil

• don’t feed a flytrap with raw meat such as hamburger, because it encourages rot


If you wish to grow a Venus flytrap as a houseplant, you will need a terrarium or other glass container with a small opening to provide the necessary humidity. Water your Venus flytrap with either distilled water or rain water, recommends Bob McMahon of the Ohio State University Agricultural Technical Institute. Chlorine and other chemicals added to tap water can be toxic to carnivorous plants. If you grow a Venus flytrap outdoors north of zone 7, you will need to bring it indoors before the first frost and provide it a cool room in which to overwinter. The Venus flytrap naturally goes dormant during the winter, so it will require a location with less light and cooler temperatures.

A healthy Venus flytrap will produce white flowers in the spring, but some growers remove them to preserve the plant’s energy. The plant is easily propagated by division in spring or summer.

 Venus Flytraps in the Wild
ImageImageImage
 large specimen in boggy habitat  flytrap spring flowers
Green Swamp in North Carolina


A Vulnerable Species
The popularity of the Venus flytrap as a scientific curiosity has made it a target for poachers. Any time you purchase a protected plant such as the Venus flytrap, be certain you are dealing with an ethical nursery. Ensure that the plant you buy has been grown from tissue culture and not harvested from the wild. Unfortunately, human development that entails the draining of bogs and swamps is an even more catastrophic threat than poaching to the survival of the Venus flytrap and other carnivorous plants.


Sources:
Botanical Society of America: The Mysterious Venus' Flytrap

Ohio State University: Feed Me Seymour! Carnivorous Plants All Bark, No Bite

"Venus Flytraps are Trapped in a Shrinking Natural Habitat"' Mike Baker; USA Today; Oct. 2008

Growing Carnivorous Plants by Barry A. Rice; Timber Press, 2006

Bizarre Botanicals by Larry Mellichamp and Paula Gross; Timber Press, 2010

Images:
thumbnail by CameliaTWU
partially closed leaf by Cskk
flytrap with insect inside by your neighborhood librarian
close-up of trigger hairs, flytrap in the wild and flytrap in flower by NC Orchid
Green Swamp by The_Gut


  About Gwen Bruno  
Gwen BrunoAfter spending 28 years as a teacher and librarian, Gwen Bruno is now a full-time freelance writer residing in suburban Chicago. As a preschooler, she lovingly tended a small patch of weeds in her backyard. Luckily, her parents supported her budding horticultural endeavors, and she's been gardening ever since.

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