An estimated 4,500 species of invertebrates (2,582 in Hawaii and approximately 2,000 in the continental U.S.) have been introduced. These include insects, spiders, crustaceans, molluscs--and 11 species of earthworms. The vast majority entered unnoticed on plants in soil and in water ballast from ships. A few were introduced in biological control efforts that went awry. Altogether, they cost the U.S. $23 billion a year.

Approximately 500 non-indigenous insect and mite species are pests in crops, stored-food products, and structures. In Hawaii, non indigenous insects account for 98 percent of the pest insects. In California, the 600 introduced species are responsible for 67 percent of all crop losses.

According to Pimentel, pest insects destroy about 13 percent of potential crop production, representing a value of about $36 billion in U.S. crops. Since 40 percent of the pests were introduced the researchers estimate they account for $14 billion a year in crop losses. Another $500 million in pesticides is used to control these interlopers. An additional $1.5 billion is spent each year to control introduced species in lawns, gardens and golf courses. About 360 non-indigenous insect species also cause the loss of about $2.1 billion worth of forest products each year.

Gypsy Moth
Image: Virginia Tech

GYPSY MOTH (Lymantria dispar) was intentionally introduced into Massachusetts in the 1800s. It is now a major pest of U.S. forests and ornamental trees, especially oaks. The U.S. Forest Service currently spends about $11 million annually on gypsy moth control.
Wooly Adelgid
Image: Virginia Tech

WOOLLY ADELGID (Adelges piceae), an aphid, has spread thoughout the southern Appalachians over the past 20 years. It has already resulted in the loss of two native bird species from habitat destruction and the invasion by three other species.
Fire Ant
Image: North Carolina State University

RED FIRE ANTS (Solenopsis invicta) kill poultry chicks, lizards, snakes and ground nesting birds. The estimated damage to livestock, wildlife, and public health caused by fire ants in Texas is estimated to be $300 million a year,and an additional $200 million is spent annually in control. The Cornell ecologists estimate total fire ant damages in infested states at approximately $1 billion per year.
Green Crab
Image: GREGORY C. JENSEN

EUROPEAN GREEN CRAB (Carcinus maenas) gets blamed for the demise of the soft shell clam industry in New England and Nova Scotia. It also has destroyed commercial shellfish beds and preys on large numbers of native oysters and crabs. Its estimated economic impact is $44 million a year.
Zebra mussel
Image: Wayne State University

EUROPEAN ZEBRA MUSSEL (Dreissena polymorpha) is one of the most serious pests among the 88 species of non-indigenous molluscs that have taken up residence in U.S. waters. It apparently traveled to the Great Lakes from Europe in ships' ballast water and has now spread throughout the eastern U.S. Mussel densities have been recorded as high as 700,000 per square meter. They compete for food and oxygen with native species and invade and clog water intake pipes, water filtration and electric generating plants. An estimated $3 billion is spent annually for control and cleaning.
Data: Excerpted from Environmental and Economic Costs Associated with Non-indigenous Species in the United States

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