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ARKANSAS DEPARTMENT OF
ENVIRONMENTAL QUALITY
SOME FACTS ABOUT
EARTHWORMS
R E C Y C L I N G B R A N C H
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There are several thousands of species of earthworms, including those that live in water (aquatic) as well as those that
live on land (terrestrial). Terrestrial earthworms can be classified as litter dwellers (epigeic), shallow-soil dwellers
(endogeic) and deep burrowers (anecic). Litter dwellers are the worms that tend to do best in compost bins.
Common names may be confusing. Eisenia foetida, the worms most mentioned for composting, are commonly called
red wigglers, but may also be called redworms, tiger worms, manure worms or brandling worms. Lumbricus rubellus
are also called red wigglers, but are more often called red worms or redworms. Eisenia andrei are most often called
red tiger worms, but can also be called just tiger worms. All of these worms will do well in a compost bin.
Earthworms are 90 percent water and have no bones. Instead their structure is provided by a “hydrostatic skeleton,”
coelmic fluid (fluid within the body cavity) held under pressure and surrounded by muscles.
Earthworms have no lungs, but they do breathe oxygen. They exchange oxygen through their moist skin. If an earthworm’s skin dries out, it will suffocate and die.
Earthworms have five hearts, although they are not four-chambered hearts like ours. Instead, they are five pairs of
enlarged blood vessels with valves that prevent the blood from backing up. Like human blood, earthworm blood has
iron-rich hemoglobin as its base and is red in color.
Earthworms have no eyes, but sensory cells in their skin help them detect light and they will always move away from
it if possible. Earthworms will become confused and eventually become paralyzed, dry out and die if exposed to light
for too long.
Earthworms have no ears, but they can feel vibrations in the ground. This helps them sense predators moving toward
them through the soil.
Earthworms have bristles, called setae, along the bottom of their bodies which help them move. These bristles can be
pulled in like a cat’s claws.
Earthworms are 82 percent protein and are a food source for many people around the world.
Earthworms live where there is food, moisture, oxygen and a favorable temperature. If they don’t have these things,
they will go somewhere else. Keep this in mind when building and maintaining your worm bin.
Respiration
Unlike humans, worms have no lungs. They respire
(breathe) through the entire surface of their bodies.
Oxygen dissolves in the moisture on the worm’s
body. Oxygen then passes into the body and the
bloodstream. Worms need enough moisture to keep
their skin wet, but not enough to drown them.
Worms are not aquatic animals, but some species
can live under water if there is enough oxygen dissolved in the water. Without moisture, however, the
worms will die.
Ingestion
How much garbage can worms eat? A worm can
consume about half of its weight each day. A
pound of worms might eat one-half pound of food
in a day, depending on environmental conditions.
The bedding in the worm bin disappears as it, in
addition to the food, is consumed and converted
into castings.
Digestion
Microorganisms such as bacteria and fungi aid
worms, which do not have teeth, by breaking down
pieces of food. Bacteria act as digesters, and fungi
break down cellulose. A worm’s mouth has a small
sensitive pad of flesh, called the prostomium, that
protrudes above its mouth and stretches out to
sense suitable food particles. Worms have a muscular gizzard, which functions similarly to that of
birds. Small grains of sand and mineral particles
lodge in the gizzard. Muscular contractions compress these hard materials against each other and
the food, mix it with some fluid, and grind it into
smaller particles. Undigested matter such as soil
will pass through the worm’s long intestine. The
tiny, dark-colored masses the worms deposit are
called worm castings. Other names for worm castings are worm manure or worm feces (“poop” to
children). Castings contain thousands of bacteria,
humus and many nutrients that help plants grow.
Locomotion
Worms move by contracting and relaxing their
muscles in waves, alternating between circular and
long muscles. Contraction of the circular muscles
forces the worm’s body forward. Then the long
muscles contract, drawing the tail end of the worm
toward the skinny front end. When the long muscles contract, the circular muscles relax, causing the
worm to become thick. To keep from skidding during movement, tiny bristles called setae act as
brakes to hold part of the worm’s body against the
surface. The worm moves forward and backward in
similar ways.
Reproduction
Earthworms are hermaphrodites, equipped with
both male and female organs. They reproduce by
joining together with mucus produced at the clitellum, a round band around the midsection. Sperm
passes from each worm to the other’s sperm storage
sac. As the mucus hardens, a cocoon forms. As the
worms back out of the cocoon, eggs and sperm are
deposited into it. The cocoon seals itself, fertilization takes place inside the cocoon, and within a few
weeks, two or more baby worms hatch. Red wigglers take approximately two to three months to
mature. A red wiggler is mature (and ready to reproduce) if it has a clitellum.
When temperature, moisture and food are favorable, a mature earthworm can mate and produce two
to three cocoons per week. Cocoons look like tiny
lemons, starting out white and ending up red-brown
before hatching. The cocoons take at least three
weeks to mature, and two to four baby worms hatch
out of each cocoon. After hatching, baby worms are
nearly transparent and weigh three milligrams or
less.
Although worms are very prolific, they will automatically keep their numbers in check in a worm box.
DON’T DO IT!
Contrary to folklore, if a worm is cut in half, the halves do not regenerate. If a tiny part of the worm is cut off, it can heal and eventually grow
back. However, this ability to regenerate is limited to a few segments
from the tail end and even fewer segments from the head end. If you cut
a worm in half, you’ll kill it.
Photo © Amy Stewart (www.amystewart.com)
Revised July 2014