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

Filter Total Items: 19
Date published: April 28, 2015

Burmese Python Habitat Use Patterns May Help Control Efforts

EVERGLADES NATIONAL PARK, Fla.— The largest and longest Burmese Python tracking study of its kind -- here or in its native range -- is providing researchers and resource managers new information that may help target control efforts of this invasive snake, according to a new study led by the U.S. Geological Survey.

Date published: April 16, 2015

Genetics Provides New Clues about Lionfish Invasion

New genetic data suggest the red lionfish invasion in the Caribbean Basin and Western Atlantic started in multiple locations, not just one as previously believed, according to a new study led by the U.S. Geological Survey.

Date published: May 25, 2014

Climate Change Accelerates Hybridization between Native and Invasive Species of Trout

Scientists have discovered that the rapid spread of hybridization between a native species and an invasive species of trout in the wild is strongly linked to changes in climate.

Date published: July 12, 2012

Asian Carp Pose Substantial Risk to the Great Lakes

Asian carp pose substantial environmental risk to the Great Lakes if they become established there, according to a bi-national Canadian and United States risk assessment released today.

Date published: January 30, 2012

Severe Declines in Everglades Mammals Linked to Pythons

HOMESTEAD, Fla. -- Precipitous declines in formerly common mammals in Everglades National Park have been linked to the presence of invasive Burmese pythons, according to a study published today in the Proceedings of the National Academy of Sciences. 

Date published: March 14, 2011

Extent and Speed of Lionfish Spread Unprecedented

The rapid spread of lionfishes along the U.S. eastern seaboard, Gulf of Mexico, and Caribbean is the first documented case of a non-native marine fish establishing a self-sustaining population in the region, according to recent U.S. Geological Survey studies.

Date published: May 4, 2006

USGS Finds One in Four Fishes is Non-Native in 12 Western States: Non-Natives Flourish in Half of Streams Studied

One of every four fishes in streams of 12 western states is non-native, according to a U.S. Geological Survey (USGS) study published in November 2005 in the North American Journal of Fisheries Management. And, researchers found, it´s not just that there are a lot of non-native fishes but they are also widespread...

Filter Total Items: 19
August 12, 2012

Yazoo! Flying Carp!

U.S. Geological Survey scientists encounter Asian flying carp on the Yazoo River, Mississippi.

Attribution: Water Resources
Image:  Collared Feral Pig Ready for Release
January 30, 2012

Collared Feral Pig Ready for Release

A boar of about 260 pounds near Pecan Island, Louisiana, with LOTEK tracking collar attached and ready for release.

Attribution: Ecosystems
Adult male mouflon stands broadside of the camera in a grassy field
June 12, 2008

Adult male mouflon stands broadside

An adult male mouflon stands broadside to the camera in a grassy field on Hawai‘i Island. Mouflon were introduced to Hawai‘i for trophy hunting in the 1950s. 

Image: Adult Lionfish
October 1, 2004

Adult Lionfish

Adult lionfish, approximately 250 mm total length.

Attribution: Ecosystems
Image: Invasive Zebra Mussels
July 22, 2003

Invasive Zebra Mussels

The zebra mussel (Dreissena polymorpha) is a small, non-native mussel originally found in Russia. In 1988, this animal was transported to North America in the ballast water of a transatlantic
Attribution: Ecosystems
Image: Invasive Lionfish Removal

Invasive Lionfish Removal

The invasive red lionfish (Pterois volitans) waits to be hauled to the surface, where it will eventually be used by NOAA to conduct lab studies on lionfish reproductive biology, age, and growth.

Attribution: Ecosystems
Photo of WERC scientist Jon Keeley in southern California chaparral habitat

Jon Keeley with Chaparral and Invasive Grasses

Used with permission from Richard W. Halsey, California Chaparral Institute.