APHIS FACTSHEET

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United States

Department of

Agriculture

Animal and

Plant Health

Inspection

Service

October 1999

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

has 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 aquatic organisms often

reduce the economic productivity and ecological

integrity of U.S. agriculture and natural resources.

The most 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).

Additionally, numerous invertebrate invasive species

have also become established in the United States.

Examples include zebra mussels, imported fire ants,

Africanized honey bees, and many other insects. In

Hawaii and some mainland States, feral pigs, goats,

and cats have severely impacted natural and

environmental resources. Feral animals are

domesticated animals that have escaped and

become wild, including their offspring born in the wild.

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. The very

establishment of a harmful invasive species

diminishes biological diversity because, as certain

species disperse to more places, the originating and

invaded areas become more alike biologically.

In 1993, Congress’ 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 include: melaleuca (a wetlands tree),

gypsy moth, spruce bark beetle, zebra mussel, larch

canker, chestnut blight, and pinewood nematodes.

Fear of the incursion of other harmful invasive

species, such as the brown tree snake, is increasing.

Conservation experts have found that in the

United States, invasive alien plant infestations cover

100 million acres and are spreading at a rate of 14

percent per year—an area twice the size of Delaware.

Recent studies have also revealed that San Francisco

Bay is invaded by a new exotic species on the

average of once every 12 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 their movement and

release can be an unintentional byproduct of

cultivation, commerce, tourism, or travel.

Many species enter the United States each year

as contaminants of commodities. Agricultural

produce, nursery stock, cut flowers, and timber can

harbor insects, plants 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 shrimp pathogens and parasites have

been introduced into the United States on infected

stock for aquaculture. Crates and containers can

harbor snails, slugs, mollusks, beetles, and

microorganisms. Military cargo transport also brings

in harmful species, such as the Asian gypsy moth

and brown tree snakes. Ballast water that is released

from ships as cargo is loaded or unloaded has

brought in several destructive aquatic species.
Safeguarding the United States from

Invasive Species

On February 3, 1999, President Clinton signed

Executive Order 13112 enhancing and coordinating

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 efforts of the involved Federal

agencies. This Executive order provides new 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 our biological

resources from being introduced and becoming

established in the United States.

Both ecosystems and the individual species

within them 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 controls 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 including detecting,

eradicating, managing, or controlling specific pests

that have become established. Third, certain

endangered species need special protection against

a host of attackers. Endangered species are rescued

from illegal trade at ports of entry and protected

within the United States. Invasive species can be a

threat to indigenous endangered species. Finally,

human populations need help in coping with the

needs of certain organisms, such as migratory birds,

so that human activity and wildlife can coexist.

APHIS’ Role in Safeguarding

Many plants and plant 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 harmful.

Sophisticated methodologies measure the level of

risk. This information assists APHIS in 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 other professionals

have been 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 invasive species that

are potential plant pest risks. APHIS is also

reviewing its statutory base for the regulation of

noxious weeds that have entered the United States.

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 treaties directly

or indirectly related to invasive species. These

include the International Plant Protection Convention,

Convention on Prevention of Diseases in Livestock

(United States-Mexico), Convention on International

Trade in Endangered Species of Wild Flora and

Fauna, Convention for the Protection of Migratory

Birds (United States-Canada), and Convention for the

Protection of Migratory Birds and Game Animals

(United States-Mexico).

Domestic laws that APHIS implements include

the Plant Pest Act, the Plant Quarantine Act, the

Federal Noxious Weed Act, certain provisions of the

Federal Seed Act, and the Honeybee Act.

The following are examples of APHIS’ eradication

and control programs for invasive species.
The U.S. Department of Agriculture (USDA) prohibits

discrimination in all its programs and activities on the basis of

race, color, national origin, gender, 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, 14th and

Independence Avenue, SW, Washington, DC 20250–9410 or call

(202) 720–5964 (voice and TDD). USDA is an equal opportunity

provider and employer.

Asian longhorned beetle, which kills hardwood

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

warehouses in several U.S. cities. APHIS is working

to develop and 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 has initiated

eradication campaigns to eliminate Asian longhorned

beetle from areas where they have been detected.

Yellow star thistle is the most problematic weed

in California. APHIS has established a partnership

with the California Department of Food and

Agriculture and USDA’s Agricultural Research

Service to fund a scientist position at the Albany

quarantine facility in California. This individual will

work on a wide variety of issues including yellow star

thistle control.

Brown tree snakes have caused the decline of

many native wildlife species (particularly birds), large

economic losses from power outages, and hazards to

human safety from bites. The Department of Defense

provides $1 million to APHIS each year to conduct

the control program on Guam. APHIS has identified,

contacted, and established cooperative service

agreements with nearly every company and agency

involved with the shipment of cargo from Guam.

Cargo shipments are potential risks for the snakes to

be moved to Hawaii and other places currently free of

brown tree snake. Other APHIS cooperators include:

Guam International Airport Authority, Guam Power

Authority, Commercial Port Authority, and

approximately 17 privately owned processing

warehouses. In addition to cooperative agreements

and trapping efforts, Jack Russell terriers are used to

detect snakes in air cargo. To further efforts,

personnel at APHIS’ National Wildlife Research

Center are developing and testing potential brown

tree snake toxicants, repellants, and attractants.

Nutria, once a fur market resource, escaped into

Louisiana’s coastal marshes in the late 1930’s. In

addition to damaging private property by destroying

ornamental plants and excavating burrows, nutria

aggravate 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 and problems have continued to

escalate. APHIS cooperates with the Louisiana

Department of Wildlife and Fisheries, providing direct

control and technical assistance. APHIS has also

provided technical assistance to managers of the

Blackwater National Wildlife Refuge in Maryland, who

requested advice on resolving nutria problems along

the Chesapeake Bay.

Tropical bont tick is a pest of major 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 prevalent on Caribbean islands, posing a

threat to the U.S. mainland due to frequent travel and

commerce between the areas. Since 1994 APHIS,

has provided technical advice and council to the

Caribbean Amblyomma Programme. APHIS also

contributes $330,000 annually to help fund the

program.

Boll weevil is the primary insect pest of cotton

that 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 cost sharing 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.

Additional Information

For more information on APHIS’ role in managing

invasive species, please visit the APHIS Website at

www.aphis.usda.gov or contact

Andrea Morgan, APHIS Invasive Species Coordinator

USDA, APHIS

4700 River Road, Unit 39

Riverdale, MD 20737–1240

Telephone: (301) 734–3772

FAX: (301) 734–8724

E-mail: andrea.m.morgan@usda.gov