Invasive Species

Over the past 200 years, several thousand foreign

plant and animal species have become established in

the United States. About one in seven have become

invasive, leading to problems that, according to 

figures provided by Cornell University, cost the United

States more than $138 billion each year. An invasive

species is an alien species whose introduction does,

or is likely to, cause economic or environmental harm

or harm to human health. Invasive plants, animals,

and pathogens have often reduced the economic 

productivity and ecological integrity of agriculture,

forestry, and the Nation’s other natural resources.

Common vertebrate invasive species in the 

continental United States include nutria, house 

sparrows, European starlings, and commensal

rodents (roof rat, Norway rat, and house mouse). In

Hawaii and in some continental U.S. States, feral

pigs, goats, and cats have severely impacted natural

and environmental resources. Additionally, numerous

invertebrate invasive species have become 

established in the United States, including zebra

mussels, imported fire ants, Africanized honey bees,

and Asian longhorned beetles, to name a few.

Effects of Invasive Species

Many harmful invasive species clearly impair 

biological diversity by causing population declines,

species extinctions, shifts in predator–prey dynamics,

shifts in species niches, changes in habitat, and

reductions in ecosystem complexity.

In 1993, the Congressional Office of Technology

Assessment reported that devastating invasions of

plants, insects, aquatic invertebrates, pathogens, and

other organisms have changed ecosystems and 

permanently diminished the biological diversity 

associated with them. Examples of these in the

United States and its territories include: melaleuca (a

wetlands tree), gypsy moth, spruce bark beetle,

zebra mussel, larch canker, chestnut blight, and the

brown tree snake.

Conservation experts have found that in the

United States invasive alien plant infestations cover

100 million acres (an area twice the size of

Delaware)and are spreading at a rate of 14 percent

per year. Recent studies have also revealed that the

San Francisco Bay is invaded by a new exotic

species on the average of once every few weeks.

Movement

Naturally occurring movement of species into the

United States is uncommon. Most invasive species

arrive in association with human activities or 

transport. Species can be brought into the country

and released intentionally or unintentionally through

the international movement of people, commodities,

and their conveyances.

Many species enter the United States each year

as contaminants of commodities. Agricultural 

produce, nursery stock, cut flowers, and timber can

harbor insects, plant pathogens, slugs, and snails.

Weeds continue to enter the United States as seed

contaminants. Plant pathogens sometimes arrive as

unintended contaminants of plant materials.

Fish and shellfish pathogens and parasites have

been introduced unintentionally into the United States

on infected stock destined for aquaculture. Crates

and containers can harbor snails, slugs, mollusks,

beetles, and other organisms. Military cargo transport may unintentionally bring in harmful species.

Ballast water that is released from ships when cargo

is loaded or unloaded has historically brought in

numerous unwanted aquatic species.

Safeguarding the United States from

Invasive Species

On February 3, 1999, the President signed

Executive Order 13112, requiring coordination and

enhancement of Federal activities to control and minimize the economic, ecological, and human health

impacts caused by invasive species. The Executive

Order also established a National Invasive Species

Council to oversee a management plan detailing the

goals and objectives of the Federal agencies and

departments involved.

The Executive Order builds upon existing

Federal, State, and non–government organizations to

help solidify the Nation’s protection against invasive

species and to enhance communication between all

that are involved. The National Invasive Species

Council, which the Secretary of Agriculture co–chairs,

was established by the Executive Order to develop an

overall Federal strategy for minimizing the impact of

invasive species. This goal was outlined in the

National Invasive Species Management Plan, 

published in 2001. This plan contains 57 specific

action items that Federal agencies need to address

to improve coordination, prevention, control, and

management of invasive species.

Factsheet

Plant Protection and Quarantine April 2003

APHIS
This Executive Order and its National Invasive

Species Management Plan provide impetus and

importance to the basic work performed by the U.S.

Department of Agriculture’s (USDA) Animal and Plant

Health Inspection Service (APHIS) to prevent pests

and diseases that threaten the Nation’s biological

resources from becoming established in the United

States.

Both natural pristine ecosystems and those 

modified for agriculture are vulnerable to invasive

pests and pathogens. In protecting the United States

from harmful invasive species, APHIS is responsible

for excluding and managing invasive species that can

potentially affect plant and animal health, either 

directly or indirectly. Through its activities, APHIS 

protects not only agriculture but also forest, rangeland, and wetland ecosystems. APHIS works closely

with USDA’s Forest Service and the U.S. Department

of the Interior’s Bureau of Land Management,

National Park Service, and Fish and Wildlife Service.

APHIS is also actively engaged in controlling certain

types of invasive species and vertebrate pests that

affect native ecosystems, rather than agricultural

resources. Certain specific activities focus on 

protecting and managing endangered species as well

as migratory bird populations.

The first and most effective means of protection is

through exclusion or prevention of intentional or 

unintentional entry of harmful invasive species. A

second strategy uses tactics that include detecting,

eradicating, managing, or controlling specific pests

that have become established. Third, certain endangered species need special protection against a host

of human and biologically induced stressors.

APHIS’ Role in Safeguarding

Many plants or their associated germplasm are

imported intentionally for propagation and use.

Organisms are intentionally brought in for biological

control, including insects, fish, snails, plant pathogens,

and nematodes. APHIS has a permitting system to

assess organisms for plant pest risk or risk to 

animals. Entry may be authorized under certain 

conditions. Scientifically based methods of risk

assessment allow APHIS to make informed decisions

as to the potential for risk to the environment. APHIS

has biological scientists skilled in making the assessments necessary to issue or deny a permit.

Risk assessment uses scientific information to

determine numbers and kinds of organisms that have

the potential to become established and become

harmful. Sophisticated methodologies are used to

estimate the level of risk. This information assists

APHIS with decisions to issue permits for introduction,

interstate movement, and release into the environment of organisms that can be beneficial to society.

In response to, and in anticipation of, increased

movement of people and biological products and

organisms (both intentional and unintentional, legal

and illegal), APHIS scientists and risk assessors are

developing new risk assessment methodologies, regulatory processes, and assessments of effectiveness in

the agency’s programs. These efforts include the

development of specific regulations that outline the

types of scientific information needed to obtain a permit to import and/or release into the environment

non–native species that are potential plant pest risks.

In addition, APHIS is reviewing and assessing the

effectiveness of its activities for safeguarding the

United States from invasive species.

APHIS is responsible for implementing several

multilateral and bilateral international agreements

directly or indirectly related to invasive species. These

include, but are not limited to, the International Plant

Protection Convention, Office International des

Epizooties, North American Plant Protection

Convention, North American Free Trade Agreement

(NAFTA), Convention on Prevention of Diseases in

Livestock, Convention on International Trade in

Endangered Species of Wild Flora and Fauna,

Convention for the Protection of Migratory Birds, and

Convention for the Protection of Migratory Birds and

Game Animals.

Domestic laws that APHIS implements include the

Plant Protection Act, Animal Health Protection Act,

Federal Seed Act, Honeybee Act, and the Agricultural

Bioterrorism Protection Act. The following are examples of some of APHIS' domestic prevention, eradication, and control programs for invasive species:

Asian longhorned beetle, which kills hardwood

trees, has been detected in New York, Chicago, New

Jersey, and warehouses in several other U.S. cities.

APHIS is working to implement new regulations for

incoming solid wood packing material and has issued

an interim rule for solid wood packing material coming

from China. These initiatives will minimize the likelihood of future Asian longhorned beetle introductions.

Additionally, APHIS works with local agriculture officials in eradication campaigns to eliminate Asian longhorned beetle from areas where it has been detected.

The glassy–winged sharpshooter, an invasive

insect detected in California in the early 1990s, carries with it the plant bacterium Xylella fastidiosa,

which causes a variety of plant diseases, including

Pierce’s disease. This disease has already caused

multi–million–dollar losses of California grape crops

and continues to pose a major threat to the grape,

raisin, and wine industries, and the tourism associated with them. APHIS has allocated millions of dollars

to help California implement a statewide management

program for inspection of inter– and intra–state nursery stock; to establish multi-county pest management

areas; and to conduct aggressive public outreach to

educate growers and others about this pest problem.
Brown tree snakes have eliminated 10 of the 13

native bird species and most lizard species and bat

species on the island of Guam. This native of the

South Pacific and Australia is responsible for large

economic losses from damaged electrical lines and

resultant power outages, and poses hazards to

human safety (especially children) from bites. The

Departments of Defense and Interior provide 

$1 million and $400,000 respectively, to APHIS each

year to prevent the spread of the snake off island. As

part of this effort, APHIS has established cooperative

service agreements for snake control with nearly

every company and agency involved with the shipment of cargo from Guam. Aircraft, ships, and their

associated cargo pose the highest potential risks for

snake introduction into Hawaii and other places 

currently free of the brown tree snake. Snake populations are reduced using specially designed traps and

hand capture. In addition Jack Russell terriers are

used to detect snakes in outbound cargo. To further

efforts, personnel at APHIS’ National Wildlife

Research Center continue to develop and test brown

tree snake toxicants, traps, barriers, repellants, and

attractants. Other APHIS cooperators include: Guam

International Airport Authority, Guam Power Authority,

Port Authority of Guam, U.S. Geological Survey, and

19 privately owned cargo–processing warehouses.

Nutria, a furry rodent that was once considered a

fur market resource, escaped into Louisiana's coastal

marshes in the late 1930s. Since that time, the market collapsed and less than 200,000 animals are now

caught each year. In addition to damaging private

property by destroying ornamental plants and excavating burrows, nutria contribute to coastal erosion,

which already destroys as much as 40 square miles

of Louisiana's coastal marshes each year. Nutria can

be found from Texas to Florida on the Gulf Coast and

as far north as Maryland on the Atlantic Coast. Their

geographic range continues to expand, essentially

unchecked, into new areas. APHIS cooperates with

the Louisiana Department of Wildlife and Fisheries,

providing direct control and technical assistance.

APHIS also provides technical assistance to managers of the Blackwater National Wildlife Refuge in

Maryland, in helping to resolve nutria problems along

the Chesapeake Bay and its tributaries.

Tropical bont tick is a pest of concern to the

United States because it can carry a parasite that

causes heartwater disease—a threat to domestic livestock. This tick belongs to the genus Amblyomma

and is present on several Caribbean islands, posing a

threat to the U.S. mainland because of frequent travel

and commerce between the areas. APHIS provides

technical advice and counsel to the Caribbean

Amblyomma Programme (CAP). CAP continues to

achieve successes in eliminating this livestock pest,

with four of the original nine Caribbean islands where

it was present now listed as free of the tropical bont

tick. Working with livestock owners and government

staffs throughout the Caribbean, CAP has expanded

its surveillance coverage to several medium–risk

islands as a preventive measure. APHIS contributes

more than $300,000 annually to help fund the 

program, along with the United Nations’ Food and

Agriculture Organization, the International Fund for

International Development, and the European

Commission’s Caribbean Agriculture and Fisheries

Programme.

Boll weevils are the primary insect pests of 

cotton. They came to the United States from Mexico

in 1892. This pest costs U.S. farmers more than $200

million annually in control efforts and yield losses.

APHIS participates in the boll weevil eradication 

program through sharing costs with the affected

States and cotton growers and by providing technical

support. Due to the overall success of the program,

many States contribute additional funding to these

eradication efforts, reducing grower costs and 

stimulating rural economies. Today, many areas of the

United States remain free of boll weevil.

Additional Information

For more information on APHIS’ role in minimizing

the impact of invasive species, please visit the APHIS

Web site at www.aphis.usda.gov or contact:

Richard L. Orr, APHIS Invasive Species 

Coordinator

USDA, APHIS

4700 River Road, Unit 117

Riverdale, MD 20737–1240

Telephone: (301) 734–8939

FAX: (301) 734–5899

E-mail: richard.l.orr@aphis.usda.gov

For more information on the Invasive Species

Executive Order 13112, visit the National Invasive

Species Council at Web site 

www.invasivespecies.gov.

For more information on the National Invasive

Species Act, visit the Aquatic Nuisance Species Task

Force at Web site www.ANSTaskForce.gov.

The U.S. Department of Agriculture (USDA) prohibits discrimination

in all its programs and activities on the basis of race, color, national

origin, sex, religion, age, disability, political beliefs, sexual orientation, or marital or family status. (Not all prohibited bases apply to

all programs.) Persons with disabilities who require alternative

means for communication of program information (Braille, large

print, audiotape, etc.) should contact USDA’s TARGET Center at

(202) 720–2600 (voice and TDD).

To file a complaint of discrimination, write USDA, Director, Office of

Civil Rights, Room 326–W, Whitten Building, 1400 Independence

Avenue, SW, Washington, DC 20250–9410 or call (202) 720–5964

(voice and TDD). USDA is an equal opportunity provider and

employer.

United States Department of Agriculture • Animal and Plant Health Inspection Service • Safeguarding American Agriculture