Invasive Species Defined

What's Being Done

 National Invasive Species Information Center

Submodule 1: Introduction

The Bad News First…

Unfortunately, many areas of the United States have been subject to the destruction caused by particular introduced species. The worst offenders include such species as the emerald ash borer, an insect that is currently a major threat to ash trees in the midwestern and eastern US, and kudzu, a fast-growing vine that is choking out native vegetation primarily in the southeastern US.

While many introduced species cause little harm to native habitats, infestation by some species has been responsible for devastating impacts such as the destruction of habitats, the elimination of native species, and major damage to agricultural crops. For this reason, over $100 billion dollars (according to figures provided by Cornell University) are spent each year in the U.S. alone attempting to prevent infestations of invasive species and to control those that have already gained a foothold.

Left: Emerald Ash Borer (Agrilus planipennis) (photo courtesy Agricultural Research Service, USDA)

Right: Kudzu (Pueraria montana) (photo courtesy NPS)

Some statistics

• Approximately 50,000 non-native species are estimated to have been introduced into the U.S.
• Invasive species are estimated to cost about $138 billion in environmental damage and losses each year.
• Non-native plants are invading about 1.7 million acres of U.S. wildlife habitat each year.
• Yellow starthistle, an invasive plant, now dominates almost 10 million acres of once productive grazing land in northern California.
• Pigeons, considered the most serious introduced bird pests, are estimated to cost over $1 billion annually for control and damage to property.
• It is estimated that fire ants, an introduced insect species, have caused a 34% decrease in the nesting success of swallows, a ground-nesting bird.
• An introduced mollusk, the zebra mussel, reduces food and oxygen for native fauna; it also causes $100 million annually in damage to water pipes and filtration systems, and in control costs.
• Approximately 65% of the crop losses attributed to plant pathogens (primarily fungi), or $21 billion, is attributed to non-native species.

Yellow starthistle (Centaurea solstitialis) (photo courtesy NRCS Plants Database)

Asian Soybean Rust (Phakopsora pachyrhizi) is a wind-borne fungal disease recently introduced into the southern and southeastern U.S. (photo courtesy Agricultural Research Service, USDA)