Forest Preserve District of Cook County, Illinois
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Earthworms
Nature Bulletin No. 359-A   November 22, 1969
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt . of Conservation

EARTHWORMS
Consider the worm. Not as excellent bait for fish, nor as food for robins, but as Charles Darwin concluded after years of patient study and experiment: "It may be doubted whether there are many other animals which have played so important a part in the history of the world as these lowly organized creatures".

A great variety of animals affect the soil structure and soil fertility -- some tiny like mites and thrips; some large like the groundhog and other burrowing mammals -- but, in woodlands, earthworms are the most important of them all. To a lesser extent perhaps, the same is true in gardens, lawns, fields and grasslands of regions having an annual rainfall of 15 inches or more.

There are about 2200 described species of earthworms in the world. They vary from small kinds, such as the one-inch Tree Worms that live under rotting wood and bark, to the gigantic kinds found in tropical countries -- some of them seven or more feet long when fully stretched out. Some are pallid in color; some are red-brown or purple; a few are gaily colored, such as the Green-worm of Europe and North America, and a Philippine species which is mottled with bright blue. Most of them prefer alkaline soils but a few will live in acid soils and we know of two species that live in decomposing manure. Some kinds live in the wet mud of river banks; two or three thrive in the filter beds of sewage treatment plants, and there are a few that actually have gills and are entirely aquatic.

In addition to our native earthworms, several species have been introduced from Europe. All of our common kinds are strictly nocturnal and spend most of their lives underground but the big one we call the "night crawler" is typical. They have no eyes but are so sensitive to light that bright sunlight will kill them. Turn over a boulder or log and you may see several quickly draw their bodies back into their burrows. They have no ears but are extremely sensitive to vibrations such as those produced in the ground by humans or other animals approaching. They must have coolness and moisture. They live in burrows which extend straight down at first, then wind about irregularly and may terminate in a cozy chamber below the frost line, from 3 to 8 feet down, where dozens or hundreds huddle in a close- packed ball, through winter, to conserve moisture.

From spring until fall they live in the upper two feet of the soil but, unless "drowned out" by a heavy rain, in daytime they commonly lie in their burrows with their heads near the surface. On warm damp nights an earthworm, with its tail anchored in the burrow, emerges and stretches out in search of food such as leaves, winged seeds like those of the maples and elms, and grass clippings. These may be dragged down into the burrow and the soft parts eaten, or used to plug the burrow entrance and conserve moisture during hot days. Many seeds are "planted" in this way. Worms reduce the surface litter and mix it with topsoil They literally eat their way through the earth, deriving food from the rich topsoil and humus. They bring subsoil to the surface in the form of pellets or "castings" which we see around the entrances to their burrows. They mix topsoil with the mineral subsoil and vice versa. Their burrows make channels through which water, air and plant roots can pass readily into the subsoil. The work they do is prodigious.

In very favorable conditions, there may be an many as two million earthworms per acre, but none in very sandy soils. Darwin estimated that 50,000 worms per acre may carry more than 18 tons of soil to the surface in a single year.

Earthworms are eaten as a delicacy by some primitive people. Do you reckon that's how spaghetti originated ?


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