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A Closer Look at the Venus Flytrap

Digesting insects such as flies helps a Venus flytrap get the nutrients it needs to grow. (Photo credit: James H. Robinson/Photo Researchers, Inc.)

This plant, commonly called Venus fly-trap, from the rapidity and force of its movements, is one of the most wonderful in the world. –Charles Darwin

Like most plants, carnivorous species such as Venus flytraps and pitcher plants, use photosynthesis to make the food that is needed to for survival. However, unlike other types of plants, carnivorous plant species also supplement their diets by catching and digesting small animals such as insects, spiders, and slugs. Why is carnivory necessary for some species of plants and not others? Research indicates that carnivory evolved in plant species that live in soil that lack the macronutrients necessary for plant growth and survival. Most carnivorous plants live in bogs, fens, and other habitats where light and moisture are abundant, but soil nutrients such as nitrogen, phosphorus, and potassium are significantly limited.

Charles Darwin was actually the first scientist to make a detailed description of several genera of carnivorous plants. His experiments indicated that these plants use enzymes similar to those found in the human stomach to digest the captured animals. Experiments conducted by Darwin’s son Francis showed that increased plant growth was a direct effect of capturing and digesting prey.

Approximately 600 species of carnivorous plants can be found around the world. Interestingly, the majority of carnivorous plants live in North America. Among the plants found in North America is the Venus flytrap, which is restricted to a 700-mile region along the coast of North and South Carolina. These coastal areas are characterized by warm, humid, and sunny conditions. The soil is acidic and lacks the minerals and nutrients necessary for the survival of most plants.

The Venus flytrap attracts potential prey by secreting from its leaves a nectar with a sweet aroma. Located on each lobe-shaped leaf are three to six sensitive trigger hairs. When the same or more than two hairs are touched, cells on the outer surface of the leaf expands rapidly, and the trap snaps shut. At less than 100 milliseconds, this movement is among the fastest movements in the plant kingdom. The two leaves do not completely shut at first. Scientists hypothesize that this incomplete closure allows smaller insects to escape, as it would cost the plant more metabolically to digest the insect than it would benefit from the nutrients found within the prey. Secretions, such as uric acid, by the trapped insect cause the trap to close its leaves together even tighter, forming an airtight seal.

Venus flytraps are native to coastal North and South Carolina. (Photo credit: Jupiterimages/Getty Images)

Once closed, digestive glands found within the leaves secrete enzymes similar to pepsin and other proteases, which digest the soft tissues of the captured insect. The flytrap also secretes an antiseptic fluid, which kills off any bacteria or fungi and prevents the insect from decaying while being digested over a period of five to 12 days. Factors that determine how long it takes the leaves to reopen include the ambient air temperature, the size of the caught prey item, the age of the flytrap, and the number of times the leaves have trapped a prey item. After the insect is digested, all that remains is its exoskeleton. When the flytrap reopens, the exoskeleton blows away in the wind, or is washed away by rain. If a non-food item, such as a pebble or twig triggers the leaves to close, the trap will reopen after a period of 12 hours, and the undigested item will be ejected.

A leaf on a Venus flytrap does not endlessly capture insects. In fact, after only 10 to 12 partial or complete closures, the leaves remain spread open. Over the next two to three months, the leaves will continue to conduct photosynthesis, until they drop off the plant for good.

Though scientists have been studying the Venus flytrap since Darwin’s time, some mysteries remain. Among the questions yet to be answered include how exactly the leaves close. A leading hypothesis suggests that an electrical current running through each leaf lobe results in a change in fluid pressure that causes the leaves to snap shut. Further research will be required to fully understand this intriguing and unique carnivorous plant.

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