Organic Farmer February / March 2020

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a tiny lip-like appendage called a prostomium.
This is a sensory organ used to
navigate, or feel its way through the soil.
Although an earthworm has no eyes, it can
still sense light, especially with the head
end. Extended exposure to UV light will
paralyze a worm and cause it to die within
a short span of time.
An earthworm’s body is made up a series
of reddish-brown flexing segments. It uses
the segments to propel itself. Each segment
is covered with tiny bristles, called setae.
These bristles act as traction devices to
help the worm move. The setae also assist
the worm in navigation.
The Bad
Night crawlers are not indigenous to North
America. They originally came over from
Europe, and are now spread throughout
North America and Western Asia. It’s
suspected they came over in soil used as
ballast in the bottom of ships.
Still, there are many types of earthworms
that are indigenous to the US. There are
approximately 6,000 species of earthworms.
Around 120 of those species are
widely distributed around the world.
Earthworms are generally considered beneficial
to the soil, although there are times
when the presence of earthworms has a
negative effect.
After the glaciers retreated, the northern
forests evolved. The resulting ecosystem
does not benefit from earthworms.
Invasive species of earthworms from the
suborder Lumricina can have detrimental
effects on temperate forests.
These forests need thick layers of slowly
decomposing duff – such as the layer
of needles, bark and debris under pine
or fir trees. When earthworms invade
the forests, they consume and break up
the organic matter and spread it down
into the soil. This increases the cycling
and leaching of nutrients. Native forest
plants have adapted to the presence of
thick layers of slowly decaying organic
matter. With this thick layer broken up
too quickly by worms, the young plants
may face conditions in which they are
not evolved to adapt.
The change in the forest has resulted in
damages to some trees, such as sugar
maples, and to forest-floor plants such
as trout lilies, trilliums and some ferns.
Earthworms are blamed for the invasion
of Japanese barberry, and for buckthorn
overrunning oak forests.
The disappearance of forest duff equates
to the disappearance of insects and
small creatures that depend on the duff
layer for food and habitat. The loss of
insects as a food source results in a population
decline of other small creatures,
such as frogs and salamanders.
While earthworm tunnels are beneficial
to farmland and gardens with compacted
soil, the burrows in forest land
may speed the passage of water seeping
through the forest floor, which can have
a negative impact.
Eradicating earthworms from invaded
forestland is virtually impossible without
spraying pesticides, which would kill other
species as well. But organic growers with
cropland near forested ecosystems can take
measures to help prevent the spread of
earthworms. If you compost with the aide
of earthworms, you can stop using worms.
Although it may not be practical, freezing
compost material for at least a week before
spreading it will kill worms and their eggs.
The Hungry
Earthworms have the best of both worlds.
As hermaphrodites, worms are both male
and female. Although unlike slugs and
snails, they cannot self-fertilize. A worm
has a pair of ovaries and two sperm receptacles.
When the romantic mood strikes, a
worm meets up with another at the surface.
There they line up, join together and
exchange sperm.
That distinguishing pink bump around an
earthworm’s body is called a clitellum. Not
only is it the defining feature of this class
of worm, but it’s also part of the worm’s
reproductive system. After fertilization, the
clitellum forms a slime tube filled with albuminous
fluid. Albumin is a water-soluble
protein – the same protein found in milk,
blood plasma and egg white.
The worm wriggles forward out of the tube.
The tube first passes over the female pore,
which deposits eggs. As the worm continues
to crawl forward, the slime tube passes
over a male opening. The eggs are fertilized
with stored sperm from the other parent
worm. The tube closes off to form a tiny,
lemon-shaped egg case. This egg cocoon is
deposited underground. A worm produces
3-80 cocoons per year. Each contains from
1-20 fertilized eggs.
The gestation period for worms is from 2-12
weeks, depending on factors such as soil
type and temperature. Baby worms hatch
and emerge tiny, but fully formed. They
become mature enough to reproduce at 3-4
months. Night crawlers can grow to 14-15
inches and may live up to six years, although
two years is more likely.
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Organic Farmer February/March 2020