Invasive Species

Half a dozen wild hogs feeding in a field of brown grass
A woman in a U.S. Fish and Wildlife Service uniform kneeling down in a grassy area examining a small flowering plant

What are Invasive Species?

Invasive species are non-native plants, animals and other living organisms that thrive in areas where they don’t naturally live, causing economic or environmental harm, or harm to human, animal or plant health. Invasive species degrade, change or displace native habitats, compete with native wildlife, and are major threats to biodiversity.

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Invasive Species in Different Regions

An invasive species is not native to an ecosystem and likely causes economic or environmental harm, or harm to humans. It is important to note that we are talking about environmental boundaries. A species can be native to one part of the country, and cause damage somewhere else. 

Invasive Species in Alaskaman holding measuring tape while another man bends down to stake the other end of the measuring tapeInvasive Species on RefugesFeral Hogs in a fieldAquatic Nuisance SpeciesA couple dozen mussels with brown-black-and-white-striped shell together on the groundAquatic Invasive SpeciesA half dozen large silver fish jumping out of the water to a height of six feet.Injurious Species Wildlife Listingsalt=A brown salamander with a yellow spotted belly crawls on green moss.

Examples of Invasive Species

nutria standing in vegetation
Nutria
Nutria, native to South America, are large, plant-eating semi-aquatic rodents sharing some characteristics with beavers and muskrats. Since their introduction to the U.S., nutria have chewed up marshlands, like at Blackwater National Wildlife Refuge in Maryland. Nutria also damage agricultural crops and infrastructure, and carry several pathogens and parasites that can be transmitted to humans, livestock and pets.
Brownish-gray grass close-up
Cheatgrass
Cheatgrass is an introduced annual grass native to parts of Europe, Africa and Asia. It invades sagebrush, pinyon-juniper, ponderosa pine, mountain brush and other landscapes of the West. When it becomes dense and dominant, cheatgrass can alter the historic fire pattern in large, interconnected habitats. After wildfire, cheatgrass thrives and can outcompete native seedlings. Cheatgrass can also diminish recreational opportunities and decrease land values.
A golden brown snake slithering toward the camera with its right eye prominent
Brown Treesnake
The brown treesnake is native to parts of Indonesia, the Solomon Islands, New Guinea and Australia. The snake was first sighted on the Pacific island of Guam in the 1950s, feeding on lizards, birds, small mammals and eggs. Treesnakes have spread rapidly and wiped out most of Guam’s native forest birds. They also crawl on electrical lines, causing expensive power outages and electrical damage.
Stringy green vegetation being held in a person's hand
Broad Waterweed
Elodea, or Canadian waterweed, is native to much of North America but is invasive in Alaska. Elodea grows in long, trailing stems of light green leaves that form tangled masses in shallow lakes, sloughs, rivers and bays. It can block passage of salmon and other fish, as well as clog boat launches, float plane access points and subsistence hunting areas.
A close-up of a green-colored frog with brownish-colored legs on a log
American Bullfrog
Native to the eastern U.S. and Canada, the American bullfrog is establishing itself around the world as an invasive species that easily outcompetes many native animals. Mature bullfrogs may weigh more than 2 pounds and are opportunistic predators. They eat most anything, including insects, snakes, lizards, turtles, frogs, fish, rodents, bats and birds.

Our Work

In ways large and small, the U.S. Fish and Wildlife Service works to prevent, eradicate and control invasive species, using environmentally sensitive approaches. Learn more about our research and programs. 

Restoring Island EcosystemsA tall fence cuts across a lush green landscape. There is a green mountain in the background with fluffy white clouds on it.Invasive Species Prevention MOUUnderside of boot being cleaned with handheld bootbrush.Island Restoration MOUA ring-shaped offshore island after being widened and replenished during a major restoration.