Bug-eating Plants Twist Normal Order of Life

Pitcher-plant, Sarracenia purpurea

The Columbus Dispatch
July 7, 2013

NATURE
Jim McCormac

Animals are supposed to eat plants, not the other way around. Carnivorous plants turn conventional plant-animal relationships upside down. The world of meat-eating botany is strange indeed, and a few of its practitioners can be found in Ohio.

About 630 species of plants worldwide are carnivores: They attract prey, capture and kill victims, and metabolize their remains. Such a bizarre twist on the usual order of things has long captured people’s imagination. Charles Darwin published a famed treatise on carnivorous plants in 1875: “Insectivorous Plants.” Much later and far more fictitiously, the movie The Little Shop of Horrors (1960) featured Audrey the man-eating plant.

Homicidal vegetable matter might seem the stuff of science fiction, but such plants are alive and well. Perhaps the best-known is the Venus’ flytrap, which is commonly sold. Many an owner has marveled at the deadly efficiency of these active “snap-traps.” Venus’ flytraps aren’t native to Ohio, but nine other carnivorous plant species are. Most of our botanical carnivores are rare — inhabitants of imperiled habitats. Three are listed as endangered; three others, threatened.

Carnivorous plants have evolved to cope with life in hostile substrates. Most species grow in soils or water deficient in nutrients, and the plants cope by assimilating nitrogen and proteins from their victims.

The pitcher plant Sarracenia purpurea is confined to a few bogs, including Buckeye Lake’s famous Cranberry Island State Nature Preserve. Pitcher plants are “passive traps.” Their highly modified leaves form tubes that fill with rainwater. Colorful purple stripes at the leaf’s summit lure flying insects; a sweetly scented flange of tissue entices ground dwellers to scale the leaf. Once atop the deadly plant, hungry insects enter the leaf’s gaping maw. Even if the bug wises up, escape might be futile. Stiff downward-pointing hairs encourage easy entrance but deter exit. Eventually, the hairs give way to glassy-smooth interior walls, and the insect slips into the drink.

Pitcher plant “juice” is water with fatal additives. The plant secretes an anti-buoyancy enzyme that reduces the odds of victims escaping. Other chemicals accelerate decomposition and aid in assimilation of the insects’ soft parts. The leaf of a well-fed pitcher plant is full of bug sludge — the residue of scores of six-legged prey large and small.

Two species of sundews occur in Ohio, and the most frequent is the round-leaved sundew (Drosera rotundifolia), which grows on sphagnum moss in peatlands. It is a “flypaper trap.” The tiny leaves are beset with hairs that seem tipped with delicious dewdrops. Thirsty insects, duped by the plant’s tasty appearance, alight only to learn that the sundew sports the botanical equivalent of Elmer’s glue. They are stuck fast, and the leaf slowly enfolds them in a death grip, sucking the life from them.

Finally, we have six species of bladderworts, plants that feature “active traps.” Some bladderworts float in water; others grow in wet soil. All have roots that are dotted with tiny sacs. If an animal jostles a trap, guard hairs are triggered and the door pops open with lightning speed. The hapless victim is instantly sucked inside, and the door slams shut. Digestive enzymes work their magic, the animal is liquefied, and the bladder is open for business again in short order.

Naturalist Jim McCormac writes a column for The Dispatch on the first and third Sundays of the month. He also writes about nature at www.jimmccormac.blogspot.com

Round-leaved Sundew, Drosera rotundifolia