- July 25 - The air-breathing
snakehead fish found in suburban Maryland has received national
attention, but it's only one of more than 30,000 invasive species
that now call the United States home and are making life difficult
for the species that were there first.
And while the snakehead has become a national celebrity -
rightly so, with its ability to survive out of water and even
propel itself short distances across land with their fins - many
species are even more detrimental to the habitats they have
invaded. Flying Asian carp in Lake Erie, piranhas in a lake in
Iowa, and citrus long-horned beetles in Seattle are among this
"An aggressive predator such as the snakehead can be disastrous
for native wildlife," said John Morrison of WWF's Conservation
Science Program. "But the threat from an invasive species like the
snakehead is nothing new. They're everywhere. In fact, just looking
outside my office window right now, the only birds I see are
pigeons, house sparrows and starlings, all natives of Europe.
Starlings, for example, compete with native birds for cavities to
nest in. While it's probably too late to address starlings in our
environment, we should actively try to prevent other non-native
species from becoming established here."
The snakehead found in Maryland has been traced to an individual
who dumped it in the pond after it outgrew his home aquarium.
Snakeheads can grow to be a foot and a half long, live three days
out of water and prey on frogs, aquatic birds and even small
mammals. None of this is a problem in the snakehead's home range in
China where its population is kept in check by an array of
predators. But none of the snakehead's predators live in the United
"Invasives are a big problem because once they're in an
ecosystem, they can be difficult or even impossible to remove,"
continued Morrison. "Invasives thrive because they outcompete
native species, having left most of their natural predators,
competitors and diseases behind."
Invasive cost the U.S. economy $123 billion a year, according to
a Cornell University study. Weeds and diseases in crops top the
list of the most damaging invaders, costing the nation more than
$53 billion annually. Rats are next on the list, causing $19
billion a year in damages.
Invasives around the U.S.
-- West -- Found in all western states, and even in some eastern
states, the leafy spurge plant is a plague for cattle ranchers,
reducing the productivity of grazing land by 50 to 75 percent and
costing the U.S. economy $100 million each year. Leafy spurge
displaces native vegetation and sends out plant toxins that prevent
the growth of other plants underneath it.
-- East Coast -- Say goodbye to that favorite hemlock tree. The
tiny hemlock woolly adelgid, accidentally introduced in the '50s
from Japan, kills hemlocks in just four years. The threat is so
severe that hemlocks might go the way of chestnut trees, which once
accounted for nearly a quarter of the trees in eastern forests, but
were virtually wiped out by an invasive fungus around the turn of
-- Great Lakes and Mississippi -- In just 14 years, zebra
mussels have spread throughout many of the major waterways in the
central United States. Native to eastern Europe and western Asia,
the zebra mussel this year may cost $5 billion in the Great Lakes
region alone to control, according to the U.S. Geological Survey
-- Southeast -- Kudzu, a fast-growing vine from Asia that can
smother a mature tree, was brought to this country for the
Centennial Exposition in Philadelphia in 1876. Soon after, it
became a popular shade vine in the south. The U.S. government even
paid people to grow it to control erosion. Millions are now spent
trying to control it.
-- Sunbelt -- Ask any boater in the coastal Sunbelt and they
will tell you about thick carpets of hydrilla floating in rivers
and lakes. Native to Africa, Asia and Australia, the plant was
introduced to Florida where it was cultivated for the aquarium
industry. The weed now chokes waterways from California to
-- Northeast -- The wetlands of the Northeast and Upper Midwest
are today full of beautiful purple flowers. Unfortunately the
purple loosestrife flower has become a menace, sucking up water,
outcompeting native species and providing little or no habitat for
native species. The plant came to this country from Europe and is
still planted as an ornamental.
-- Hawaii and Guam -- Islands have, by far, the worst problems
with invasives. Islands often have unusual species that are
vulnerable to introduced species like the brown tree snake, which
has killed off nine of Guam's 11 native birds. In some forested
areas there are more than 12,000 snakes per square mile. More than
200 people have been treated for bites from this aggressive and
Solutions to the invasives problem are hard to come by. While
education and enforcement efforts have been effective in some
places, invasive species are a growing problem as the movement of
plants and animals increases around the world. For example, 40,000
gallons of ballast water is dumped into U.S. harbors every minute.
"Considering the billions we spend fighting the invasives that
are already here, we could do a better job preventing them from
being introduced in the first place," said Craig Hoover, deputy
director of TRAFFIC North America (TRAFFIC is a joint program of
WWF and IUCN -- The World Conservation Union). "We need to think
long and hard about how and what we move around the globe because
invasives can easily hitch a ride on planes, cars -- even on shoes
-- and cause tremendous damage."