· That depends. Here are 10 things you may want to know about
earthworms:
·
Earthworms come in a seemly
infinite variety—around 6,000 species worldwide.
·
One of the most familiar of them,
the sort you may see in your garden, is commonly known as the night crawler (it
typically surfaces after dark), the angleworm (its makes popular bait for
fishing) or the rain worm (it leaves waterlogged soil after storms).
·
Of the more than 180 earthworm
species found in the U.S. and Canada, 60 are invasive species, brought
over from the Old World, including the night crawler.
·
Lacking lungs or other
specialized respiratory organs, earthworms breathe through their skin.
·
The skin exudes a
lubricating fluid that makes moving through underground burrows easier and
helps keep skin moist. One Australian species can shoot fluid as far as 12
inches through skin pores.
· Each earthworm is both male and female, producing both eggs and
sperm.
·
They mate on the surface of the
earth, pressing their bodies together and exchanging sperm before separating.
Later, the clitellum (a collar-like organ that goes around the worm’s body the
way a cigar band does a cigar) produces a ring around the worm. As the worm
crawls out of the ring, it fills the ring with eggs and sperm. The ring drops
off, seals shut at the ends and becomes a cocoon for the developing eggs.
·
Baby worms emerge from the
eggs tiny but fully formed. They grow sex organs within the first two or three
months of life and reach full size in about a year. They may live up to eight
years, though one to two is more likely.
·
Earthworm egg cases look like tiny
lemons. When earthworms hatch, they look like tiny adults. Photo credit: U.S.
Department of Agriculture
· Full
size for an earthworm varies among species, ranging from less than half an
inch long to nearly 10 feet. The
latter monsters don’t occur in U.S. backyards—you’ll have to go to the Tropics
to see one of them. The homegrown versions top out at around 14 inches.
· The
glaciers that crawled across Canada into the northern tier of the lower 48
states during the most recent ice age wiped out earthworms in those areas.
· In
other parts of the U.S., you may find native earthworm species, but the
worms living in the regions scoured by glaciers are invaders from overseas,
brought here intentionally by early settlers on the assumption that the worms
would improve the soil, or carried accidentally in shipments of plants or even
in dirt used as ballast in ships.
· The earthworm’s digestive system is a tube running
straight from the mouth, located at the tip of the front end of the body, to
the rear of the body, where digested material is passed to the outside. Species
vary in what they eat, but by and large their devouring of fallen leaves and/or
soil allows the worms to move nutrients such as potassium and nitrogen into the
soil.
·
Also, worm movements within the
Earth create burrows that encourage the passage of air and a loosening of the
soil. Good things, right? Well, maybe not. Which brings us to 10 ...
·
10. The northern forest evolved after the glaciers retreated,
yielding an ecosystem that does not benefit from earthworms. These forests
require a deep layer of slowly decomposing leaves and other organic matter
called “duff” that overlays the soil. When earthworms
invade these forests, they quickly eat up the duff, with the result
that nutrients become less available to young, growing plants and the soil,
instead of aerating and loosening, becomes more compact.
· The combined effects of such developments have resulted in
damage to trees such as sugar maples and to many forest herbs and understory
plants, such as trillium, rare goblin ferns, trout lilies and other
forest-floor species. In some areas, oak forests have been overrun by
buckthorn, and in others the presence of earthworms has allowed the invasion of
Japanese barberry.
·
As duff disappears, so do the
insects and other small creatures that depend on it for survival, with the
result that animals such as salamanders lose a key food source and face
population declines. Earthworm burrows also may speed the passage of water
through forest soil, another change that might be a benefit to farmland or a
garden with compacted soil but that is a negative in a northern forest.