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Carnivorous Plants
Nature Bulletin No. 597-A   March 27, 1976
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation

CARNIVOROUS PLANTS
Plants, generally, are eaten by insects or furnish other food for them. But there are a few families of strange plants that, instead, "eat" insects and other small animals. About 500 species are distributed over the world, from the arctic to the tropics. Most of them have peculiar leaves that not only attract insects but are equipped to trap and kill their victims. Even more remarkable is the fact that some have glands which secrete a digestive juice that softens and decomposes the animal until it is absorbed by the plant in much the same way as your stomach digests food.

All of the carnivorous plants are small and, although occasionally a dragonfly or a tiny frog may be trapped, the victims are usually ants, flies, gnats, beetles, larvae, worms and small crustaceans. In North America most of them grow in tamarack bogs, cranberry bogs, muskeg bogs covered with sphagnum moss, and in swampy places, where the brown water is acid and deficient in nitrogen. Their feeble roots serve to supply them with water but most of their food seems to be obtained from the animal matter they absorb.

The Bladderworts, however, are aquatic plants with long sinuous stems and masses of fernlike leaves submerged in shallow ponds and swamps. Along the stems there are numerous oval "bladders" each having a small opening, surrounded by stiff bristles, with a delicate trap door inside. If a larva, pursued by a minnow, darts into a bladder he cannot get out. His body is absorbed by a great number of digestive cells that line the cavity. Several kinds of bladderworts are known to live in ponds of the Chicago region.

The Butterworts occur on wet rocks and gravelly places. These plants have rosettes of long narrow leaves, each peppered with tiny glands -- about 25,000 per square centimeter -- that pour out a sticky "butter" and digestive fluid when an insect alights upon them.

In the quaking tamarack bogs of northern Illinois and northern Indiana we find a species of the Pitcher Plants. It has a clump of hollow tubular leaves that look like pitchers with flaring mouths. They have red veins and are mottled with green and brownish purple. The flowers, on stout stalks, have five sepals, five petals, and are purplish red. The pitchers are usually full of rainwater and drowned insects that were attracted to a honey-like nectar secreted by glands on the lip. The inside of the leaf is thickly lined with slick sharp spines that point downward. An insect slides down into the water and cannot escape. His decomposed remains are absorbed by cells on the pitcher wall.

The Sundews are another family of carnivorous plants that live in bogs and there are two kinds found in the Chicago region. The sundew is a small plant with a whorl of tiny round or spoon-shaped leaves on long stalks that lie flat on the soil surface. The leaves have a glistening appearance because of the hundreds of hairs on its surface, each hair ending with a gland that exudes a sticky fluid. A gnat or a fly, attracted by this "nectar, " is stuck there. The more he struggles, the more fluid is secreted by the glands. At the same time -- and this is what Charles Darwin considered one of the most incredible and wonderful things in the plant kingdom -- all of the other hairs on the leaf bend inward and surround the insect until he is suffocated. Then a digestive juice is secreted and his remains are absorbed.

Most remarkable is the Venus ' Fly Trap, a sundew of the Carolinas, whose sensitive bristled leaves close like traps to catch and "eat" insects.


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