Carnivorous plants is the descriptive name for plants from any number of families and genera which obtain nutrients by trapping and eating bugs. Carnivorous plants evolved as intriguing variations on flowering plant species in adaptation to low-nutrient environments. Rare, beautiful and strange, the origin of these intriguing plants can be found in the necessity created by their life at the edge of marginal, fragile ecosystems.
Carnivorous plants catch, digest and absorb insects--or sometimes even small mammals and frogs. Different types of carnivorous plants trap bugs in a variety of ways. Pitcher plants' leaves fold into a deep well lined with slippery sides; insects slide in, but cannot climb out. Sundews and butterworts have flypaperlike sticky leaves. The Venus flytrap has a pair of modified leaves that snap shut when an insect lands in their grasp. Corkscrew plants snare bugs in a maze of twisting, tubular stems. Bladderworts trap minute aquatic creatures with underwater sacs which remain flat until a likely meal touches them; then they rapidly expand their sides and suck the creature in.
Carnivorous plants grow in low-nutrient environments, so trapping and eating insects is how they obtain the nutritional elements that would otherwise come from organic matter in the soil. A large number of carnivorous plants live in bog ecosystems, where there is full sunlight due to lack of tree cover, and ample water, but thin soil with limited nutrient content. The plants secrete enzymes to digest their prey, and then absorb the nitrogen and other materials that are released.
Carnivorous behavior in plants was first noted by Charles Darwin in 1875. Botanist E.B. Wilson published extensive studies of carnivorous plants in the 1890s, identifying the mechanisms by which different types of carnivorous plants entrap insects. Botanists have now identified over 600 species of carnivorous plants in nine different plant families. The Botanical Society of America attributes the diversity of carnivorous plant categorizations to convergent evolution: carnivory evolved in many separate times and locations. However, more recent DNA studies call this into question. Dr. Jan Schlauer, writing in the Carnivorous Plant Newsletter, notes that DNA sequence alignment and homology comparison studies in the 1990s resulted in recategorizing several families of carnivorous plants, indicating closer evolutionary relationships than had been previously supposed.
Fossil record evidence of carnivorous plants is sparse given their fragile and dispersed nature, so the origins of carnivorous plants must be surmised through observation of current specimens. Dr. Schlauer, a botanist at the Institute for Plant Biochemistry at Tubingen, Germany, posits the following hypothetical evolutionary course for the origin and development of carnivorous plants: Bristly sepal edges developed to aid in seed dispersal, while glands developed to secrete sticky material as an aid in pollination. Crawling insects trapped on this sticky material would be absorbed by the plants, giving them a competitive advantage over their neighbors. Plant bristles moved closer to the insect locations, better holding the snared bugs. Sensitivity and digestive functions improved over time. Spring-trap mechanisms developed as a variant on mere sticky surfaces. Dr. Schlauer notes that examples of each of these different stages of development remain in existence today.
Although there are numerous species of carnivorous plants, most are quite rare. According to the Botanical Society of America, habitat destruction and overcollecting comprise the two most serious threats to carnivorous plants. Despite their disreputable images found in cheap sci-fi movies and the Broadway play "Little Shop of Horrors," carnivorous plants present no threat to humans; in fact, some Venus flytraps from environmentally sound sources may keep your home free of flies or other undesirable insects.