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EARTHWORMS AND REDWORMS
Worms are a varied lot. You may have heard of roundworms, flatworms,
tapeworms, earthworms, and who knows what other kinds of worms.
None of them conjures up a particularly warm or pleasant feeling
in most people. Worms have low reputations in human circles, often
associated with some not-so-pleasant circumstances. But this activity
may turn all that around as you dig into the subject of earthworms.
Earthworms are members of the phylum Annelida, or ringed animals.
They are fairly simple life-forms, put together from a number
of disklike segments stuck together like a long flexible roll
of coins. Earthworms have no internal skeleton like a fish, no
hard protective exoskeleton like an insect, and no shell into
which they can withdraw. Worms are flexible, elongated bundles
of muscle, uniquely suited for life underground.
The characteristic wriggling of earthworms is accomplished by
the contraction of two kinds of muscles. When the short muscles
that circle each segment (like lots of rings on a finger) contract,
the worm gets thinner and longer. When the long muscles that connect
all the segments contract, the head and tail are pulled toward
each other, and the worm becomes short and fat. Depending on which
end of the worm is anchored, the worm can move along the surface
of the ground or through its burrow effectively in either direction,
head first or tail first.
Earthworm organs are quite different from ours, making it possible
for them to live their very different lifestyle efficiently. Earthworms
have five pairs of simple hearts that pump blood throughout the
body. They have no lungs. Instead the blood flowing close to the
worm's surface absorbs oxygen and releases carbon dioxide directly
through the moist skin (called the cuticle). For this reason earthworms
can live for some time in water if the oxygen supply is adequate.
They don't drown per se, but they may suffocate if the oxygen
content is low. This is why worms leave the soil and crawl out
on the sidewalk during a heavy rain—they are seeking oxygen.
Earthworms are not adapted to feed in water, however, so they
would starve to death in due course.
Instead of a nose, ears, and eyes, earthworms have a nervous
system throughout their bodies that controls actions in response
to environmental stimuli, such as vibrations, heat, cold, moisture,
light, and the presence of other worms. They have no brain, however,
so worms do not ponder their lowly lot in life, nor do they plan
a strategy for obtaining their next meal or crossing the sidewalk
safely.
Reproduction. Like all animals earthworms have
effective strategies for begetting their own kind. With earthworms
it is not a matter of boy meets girl, but rather a simpler matter
of worm meets worm. All worms carry two sets of sexual organs,
but they cannot fertilize their own eggs—mating is still
a necessary part of reproduction. Mature earthworms have an enlarged
band some distance from the head. This enlarged clitellum plays
an important role in reproduction.
In mating, two worms approach each other nose to nose. With their
bodies touching, they slide past each other until their heads
are a bit past the clitellum. Both worms pass sperm through an
opening located between the head and the clitellum, into a temporary
holding receptacle in the other worm. The two worms separate.
The clitellum secretes a liquid that solidifies into a flexible
tube. As the tube lengthens, the worm backs out of it. Soon the
tube covers the front part of the worm. The worm lays a few eggs
inside the tube, deposits some of the stored sperm, and withdraws
from the tube, leaving the eggs and sperm inside the tube. The
ends of the tube pinch off to form a cocoon, and the whole thing
shrinks to a tidy package about the size of a fat grain of rice.
The cocoon is left alone sitting on or just under the surface
of the soil. The worm continues to produce cocoons until the sperm
is used up. Cocoons are durable, can overwinter in cold climates,
and can wait out hot dry spells in arid environments. After 3
weeks (ideal conditions) or longer the cocoon opens, and out sallies
the next generation.
Food. Earthworms feed on decomposing organic
material, mostly vegetation, from the surface of the soil and
within the soil itself. In the process of burrowing and feeding
they process tons of soil in a typical pasture or garden, improving
the quality of soil for plants and other animals. There are some
1800 species of earthworms worldwide. Some are tiny, no more than
2 cm (1”) at maturity. At the other end of the scale are
the Australian giants that average about 3 m (10’) in length,
and the record holder, a South African gargantuan measuring 7
m (22’) in length. Not to worry—the largest earthworms
in North America are the common night crawlers, which can reach
a length of little more than 30 cm (12”).
What to do when they arrive. Worms may be kept
in shipping container for short periods. Upon arrival, mist with
water to moisten, but do not make soil wet. Worms can be kept
in the refrigerator for short periods of time. To maintain worms
for a longer period of time, keep at room temperature in diffused
light, feeding crushed dead leaves or cornmeal sprinkled over
the surface of the soil. Add rich soil (preferably humus) as needed,
and remove any mold as it appears.
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