Many people are fascinated by carnivorous plants, which defy their understanding of plants as passive, motionless organisms designed to convert sunlight into sugar. Carnivorous plants snap shut on flies or drown insects in digestive enzymes and use their bodies to make up for nutritional deficiencies. Far from the alien beings depicted in science fiction movies, carnivorous plants exemplify adaptability to hostile environments found right here on Earth.
Ecology is the study of relationships between species and their environments. Carnivorous plants exemplify the extent to which even plants--silent and immobile--rely on other species to survive. Carnivorous plants need other species not only for food but also for pollination and other helpful functions.
Carnivorous plants have developed the ability to attract, trap, kill, digest and absorb nutrients from prey. For example, Venus fly traps are lined with trigger hairs that, when touched, cause the leaves to close and lock around an insect. Special enzymes break down and digest the prey's body. Carnivory is observed in at least 600 species, according to the Botanical Society of America, and evolved independently in different plants. Plants develop carnivory in order to adapt to difficult environmental conditions, and protocarnivorous plants provide evidence of additional species developing carnivorous habits.
Carnivorous plants typically grow in challenging environments such as boggy or sandy soil, providing an important clue about the purpose of carnivory to these plants. While most plants draw nutrients from the soil, the poor soil quality means that few nutrients are available through typical means and are, instead, acquired by consuming insects and other small animals. Carnivorous plants devote little energy to developing extensive root systems as a result and, pointing to the importance of carnivory, often will not grow well or flower if they cannot capture any prey.
Carnivorous plants utilize several strategies to attract prey. Typically, flowers rely on bright colors and sweet scents to entice insects, and carnivorous plants use some of the same mechanisms. Many carnivorous plants produce nectar that attracts hungry insects, and the bright colors and patterning--the red insides of Venus fly trap leaves provide one example--trick insects into thinking they are landing on a tasty flower. Guide hairs and leaf structures also lure prey inside of carnivorous plants.
Where pollination is concerned, carnivorous plants experience a slight conflict of interest. Although they consume insects as a food source, they also need insects to carry pollen from plant to plant, and carnivorous plants run the risk of consuming their benevolent pollinators. In order to enjoy the best of both worlds, carnivorous plants have developed adaptations that limit the likelihood of pollinator becoming prey. Some species, such as pitcher plants, bloom before the trap is active. Many extend their flowers above the trap on long stalks, minimizing the risk that a pollinator will fly from a flower to a sticky leaf.
Habitat destruction, loss of bog land, tight control of naturally occurring wildfires and over-collection all threaten carnivorous plant species, causing even some of the most common species to become rare sights. Donald E. Schnell, author of "Carnivorous Plants of the United States and Canada," estimates that destruction of wetland habitats to better accommodate human activities is the No. 1 risk to carnivorous plants.