Earthworms
Earthworms are one of the least understood and by some accounts the most serious threats to our native woodlands. Rich Pouyat of the U. S. Forest Service summarizes the problem from a scientific, somewhat detached, point of view in the Forest Symposium Proceedings http://www.njaudubon.org/Conservation/ForestSym.html
But
it is not hard to find experts who are gravely concerned about the impact of non-native earthworms on forest soil. Rob Jennings,
Morris County Park System biologist, is one. He states that there is not a
single native earthworm anywhere in
An article in the New York Times Garden Section on
The New York Times
<http://www.nytimes.com/>
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In the Garden
The Dark Side of a Good Friend to the Soil
By ANNE RAVER
I’VE always thought of worms as my friends, until I
started talking to
ecologists who have been
studying their voracious appetite for leaves.
“Your grandmother was wrong all these years,” said Dennis
Burton, an
ecologist at the
plants they are a large and
growing menace. In an agricultural field or
a vegetable garden, worms help
decompose organic matter, churning
nutrients back into the soil.
Their constant tunneling aerates the soil,
creating pathways for air, water
and plant roots.
But in forests in the Northeast and parts of the
proliferating and consuming
leaves at such a pace that they are actually
destroying the duff, the thick
leaf litter that nourishes tree
seedlings, prevents erosion and
protects woodland plants from disease
and insects.
They are wreaking havoc in woodland gardens, too. Barbara
and Robert
Tiffany, who tend four acres of shade-loving plants at
their home,
MillFleurs, in
four-foot-wide hostas shrink to half their size.
The Tiffanys first noticed that
their hostas were shrinking two years
ago. This was a crisis: they had
promised to show off their 1,100 hosta
cultivars to the American Hosta Society at its national convention last
June in
“I had no idea what was happening,” Ms. Tiffany said.
They thought their water might be the problem, so they
had it tested.
But the water was fine. Then they noticed “gazillions of
worms,” Ms.
Tiffany said. “Every time I would stick a trowel into the
soil, worms
would pop up or skitter away.
They were so energized, not like the worms
of my childhood.”
Mr. Tiffany did a little research and learned that the
Northeast and the
to Cindy Hale, a scientist at
the
species that are invading the
Northeast.
The Tiffanys realized, in
retrospect, that they had been helping the
worms proliferate by carting in
mulch for paths and top-dressing plants
with compost.
They recalled digging up one prized hosta,
a four-footer that had been
reduced to two feet, and
counting 19 worms as they fell from its roots.
The roots, normally so fleshy and vigorous, were stunted
and sort of
shredded, “as if something had
eaten them,” Ms. Tiffany said.
“Earthworms were not meant to be in a forest,” said Anne
Bower, a
conservation biologist at
northern forests evolved without
worms. “Their decomposers are fungi,
microflora
and fauna, which release nutrients very slowly,” she said.
rocks and soil, for ballast. The
settlers brought plants, too, which
carried worms and their eggs in
plant roots. Over the centuries, of
course, imported plants added to
the exotic worm population; so did the
fishermen who tossed their bait
worms along the banks of streams and lakes.
In fact, the night crawler, Lumbricus
terrestris, native to
favorite for baiting fish, is a
big eater in the forest.
“It’s an anecic species, a deep
diver,” Mr. Burton said. “It burrows
deep into the soil, pulling leaf
litter with it.”
Another invasive worm, an Asian species, Amynthas hawayanus, is epigeic,
meaning it stays close to the
earth’s surface, living in the topsoil and
the duff layer.
“It’s like a rototiller running
around the surface of the forest,” Mr.
Both these worms, among others, have higher populations
in urban and
suburban areas than in rural
areas. This makes sense, because they first
came in through seaports and are
often spread by gardeners who not only
purchase their plants but also
trundle mulch and compost into their
woodland gardens.
The Asian genus, Amynthas, was
first noted in
in the late 1980s by ecologists
working for the
Studies in
forests in a 100-mile radius of
These worms change the very chemistry of the soil,
because their
gizzards emit calcium carbonate,
which acts like lime on acid soil,
making it more alkaline. That
may be nice for corn and sunflowers, but
it is not good for azaleas and
oaks, which thrive in acid soil.
The worms are also breaking down organic matter so
quickly that the
nutrient overload is injuring
plants and running off into streams and
lakes. Invasive plant species,
like stiltgrass and garlic mustard, which
thrive on heavy nitrogen, then
move in.
How do you find out if you have too many worms?
Look for signs of invasive worms, such as a thinning
forest floor or
even eroded open spaces. Another
sign is a noticeable lack of spring
ephemerals like trillium,
mayflowers and trout lilies, which are
disturbed by all these tiny
plows shifting the microbial community from
fungal to bacterial.
To test for worms, mark off a section of your woodland
garden or forest
about three feet square. Then
wait for a heavy rain (this test will not
work in dry soil).
If the soil is moist, apply a hot Chinese mustard
solution, made by
mixing two cups Chinese mustard
with 10 ½ quarts of water. Sink five
coffee cans, tops and bottoms
removed, about an inch into the ground of
the marked area, then pour the
mustard solution into the cans.
“The mustard solution will go straight down and the worms
will come up,”
Ms. Bower said.
If more than five worms pop out, you have a problem. In rural areas Ms.
Bower’s researchers have found only about two worms per
three square
feet; “in the city we’re getting
89,” she said.
Ms. Bower and Mr. Burton have been testing various
organic controls,
like tobacco, walnut shells and
pine needles. They were not effective.
Sulfur pellets, however, mixed with oak leaf mulch, which
is acidic,
showed promise. Simply follow
the directions on the back of the sulfur
bag, and do not apply more than
is recommended. (Soil that is too acidic
will have its own problems.)
Then spread out a couple of inches of the
oak leaf mulch. The Department
of Agriculture lists earthworms as
beneficial organisms, so using a
pesticide to kill them is technically
illegal.
To avoid having so many worms in the first place, be sure
not to feed
them by spreading wood chips or
compost in paths in the forest. Do not
toss grass clippings, another
favorite worm food, next to the woods,
either. And do not toss out
fishing worms or red wrigglers by throwing
them on the ground or in a pond
(they do not drown).
If worms are destroying your woodland plants and you have
no choice but
to kill them, they can be put in
alcohol, frozen or collected in a bag
and sent to the landfill.