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 ?