What is an invasive species and why are they a problem?

An invasive species is an introduced, nonnative organism (disease, parasite, plant, or animal) that begins to spread or expand its range from the site of its original introduction and that has the potential to cause harm to the environment, the economy, or to human health.

A few well-known examples include the unintentional introduction of the West Nile virus, chestnut blight, the South American fire ant, zebra mussels, Burmese pythons, and sea lamprey. These are in addition to the intentional introductions of salt cedar (Tamarisk), kudzu vine, house sparrows, starlings, and nutria.

More than 6,500 of these harmful, non-native species cause more than 100 billion dollars in damage each year to the U.S. economy. Costly effects include crop decimation, clogging of water facilities and waterways, wildlife and human disease transmission, threats to fisheries, increased fire vulnerability, and adverse effects for ranchers and farmers.

Learn more: USGS Invasive Species Program

Related Content

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Are there invasive reptiles other than Burmese pythons in the United States that people should be concerned about?

Free-ranging reptiles representing dozens of species from around the world are detected in the United States in any given year, usually as a result of escape or illegal release. Fortunately, many of these individuals fail to establish reproductive populations, but all non-native species can potentially pose risks when introduced. Florida is a...

What are the potential effects of snakeheads to our waters?

During all of their life stages, snakehead fish compete with native species for food and habitat. A major concern is that snakeheads might out-compete (and eventually displace) important native or other established predatory fish that share the same habitat. As adults, snakeheads can be voracious predators. Should snakeheads become established in...

How have invasive pythons impacted Florida ecosystems?

Non-native Burmese pythons have established a breeding population in South Florida and are one of the most concerning invasive species in Everglades National Park. Pythons compete with native wildlife for food, which includes mammals, birds, and other reptiles. Severe mammal declines in Everglades National Park have been linked to Burmese pythons...

Are invasive snakes dangerous?

Free-ranging snakes representing dozens of species from around the world are discovered in the United States in any given year, usually as a result of escapees or releases from the pet trade, but most of these don't appear to have established a reproductive population. Any animal can be problematic when released in places where it is not native...
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Date published: November 13, 2018

How Hurricanes Michael, Florence May Have Spread Nonnative Species

USGS’ preliminary storm trackers show potential for subtle damage in natural areas

Date published: April 25, 2018

Invasive Cuban Treefrogs Leap Out of Florida, Establish First Known Population in Louisiana

A population of exotic invasive Cuban treefrogs has been discovered in New Orleans, more than 430 miles (700 kilometers) from the nearest known population in Florida, making this the first known breeding population in the mainland United States outside that state, reports a new study by the U.S. Geological Survey. 

Scroll down to hear and download calls of Cuban treefrogs and two native treefrogs.

Date published: April 23, 2018

USGS Tracks How Hurricane Floodwaters Spread Non-Native Freshwater Plants and Animals

Hurricanes Harvey, Irma, Maria, and Nate may have spread non-native freshwater plants and animals into new water bodies, where some of them can disrupt living communities or change the landscape.

Date published: September 6, 2017

Wildfire and Invasive Species Drives Increasing Size and Cost of Public Land Restoration Efforts

An examination of long-term data for lands managed by the Bureau of Land Management finds that land treatments in the southwestern United States are increasingly large, expensive and related to fire and invasive species control.

Date published: August 23, 2017

Invasive Pest May Not Be Only Cause of Recent Louisiana Marsh Die-off

A non-native insect infestation may not be the only factor involved in the ongoing die-back of a marsh grass in the Mississippi River’s “bird foot delta,” the ecologically and economically important part of coastal Louisiana where the river meets the Gulf of Mexico.

Date published: January 11, 2017

A Breakthrough in Controlling Invasive Fish

On a windy July morning on Lake Superior’s Whitefish Bay, fisherman Ralph Wilcox of the Sault Ste. Marie Tribe of Chippewa Indians and his son, Dan, netted 300 pounds of wriggling whitefish. The mild-flavored salmon relative is served in restaurants, in smoked fish spreads, and as gefilte fish at Passover. However, two of the fish in the Michigan fishermen’s nets were badly wounded.

Date published: November 30, 2016

Around 600 Non-Native Mountain Goats Now Roam the Olympic Mountains

Population has Increased 8 Percent a Year Since 2004

Date published: November 16, 2016

USGS Study Reveals Interactive Effects of Climate Change, Invasive Species on Native Fish

A new USGS study shows non-native Brown Trout can place a burden on native Brook Trout under the increased water temperatures climate change can cause.

Date published: July 28, 2016

Controlling Those Suckers Known as Sea Lamprey

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Date published: June 29, 2016

In Hot Water: Climate Change is Affecting North American Fish

Climate change is already affecting inland fish across North America -- including some fish that are popular with anglers. Scientists are seeing a variety of changes in how inland fish reproduce, grow and where they can live.

Date published: December 10, 2015

Continued Decline of the Northern Spotted Owl Associated with the Invasive Barred Owl, Habitat Loss, and Climate Variation

CORVALLIS, Ore. – Northern spotted owl populations are declining in all parts of their range in the Pacific Northwest, according to research published in The Condor. Based on data from 11 study areas across Washington, Oregon and northern California, a rangewide decline of nearly 4 percent per year was estimated from 1985 to 2013.

Date published: October 29, 2015

Invasive Northern Snakehead Carries Bacteria as Bad as its Bite

The invasive northern snakehead fish found in the mid-Atlantic area is now cause for more concern, potentially bringing diseases into the region that may spread to native fish and wildlife, according to a team of U.S. Geological Survey scientists.

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Picture of native and non-native plant cover in the Mojave
December 31, 2017

Invasive Annual Grass Fills the Space Between Shrubs, Mojave

An unburned low elevation community in the central Mojave where the interspaces between shrubs have been filled in with a continuous layer of Mediterranean split grass Schismus barbatus. If a fire started here it would spread much more rapidly and be far more extensive than in a low elevation community where the interspaces are rocky or bare.

Invasive Burmese Python
February 1, 2017

Invasive Burmese Python

Invasive Burmese python in the Greater Everglades Photograph credit: Brian Smith, USGS

Invasive Phramites
December 31, 2016

Invasive Phragmites

Invasive Phragmites

Image: Snakehead Fish
March 15, 2016

Snakehead Fish

Snakehead fish are originally from China and Korea, but recently they've been found in Maryland, Virginia, Arkansas, California, and Florida.

Attribution: Ecosystems
October 21, 2015

What's the Big Idea?— Turning to eDNA to Detect Invasive Species

Adam Sepulveda, research zoologist at the USGS Northern Rocky Mountain Science Center, explains a scientists at NOROCK are using environmental DNA — the identification of species through biological information they leave behind in their habitat — to detect invasive species and how this method could change the way scientists find evidence of biodiversity in ecosystems.

USGS scientist Adam Sepulveda sits with a sample of invasive northern pike in south central Alaska.
December 31, 2014

Sample of invasive northern pike in south central Alaska

USGS scientist Adam Sepulveda sits with a sample of invasive northern pike in south central Alaska.

An invasive American bullfrog with tracking device.
December 31, 2014

An invasive American bullfrog with tracking device.

An invasive American bullfrog with tracking device.  

Invasive New Zealand mud snails as seen under a microscope.
December 31, 2013

Invasive New Zealand mud snails as seen under a microscope.

Invasive New Zealand mud snails as seen under a microscope.

Image: Sea Lamprey, an Invasive Fish
August 8, 2013

Sea Lamprey, an Invasive Fish

Invasive sea lamprey prey on commercially important fish species such as lake trout, living off of the blood and body fluids of adult fish. It is one of many fish species that USGS scientists study from the USGS Research Vessel Muskie. These lamprey belong to the Great Lakes Fisheries Commission.

The R/V Muskie was temporarily moored in Buffalo, N.Y., August 8 and 9

Invasive tamarisk on the Colorado River.
December 31, 2012

Invasive tamarisk on the Colorado River.

This image is of invasive tamarisk (salt cedar) growing on the banks of the Colorado River.