An official website of the United States government.

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.


Scientific Name

Cochliomyia hominivorax (Coquerel) (ITIS; name is valid but unverified)

Common Name

New World screwworm, primary screwworm

Native To

South America and the Caribbean (CFSPH 2012)

Date of U.S. Introduction

Eradicated in the U.S. in 1966 (ARS 1992)

Means of Introduction

Could be reintroduced to the U.S. from an infested animal (CFSPH 2012)


Parasite that kills livestock and wildlife, particularly cattle (CFSPH 2012)

Current U.S. Distribution

Not currently established

Screwworm, larva(e)

Screwworm, larva(e)


Photo by Lesley Ingram

Find more images


  • USDA Protects Fruit, Vegetable and Livestock Producers with Emergency Funding to Address Exotic Fruit Fly and New World Screwworm Outbreaks

    • Dec 15, 2023
    • USDA. Animal and Plant Health Inspection Service.

    • USDA's Animal and Plant Health Inspection Service (APHIS) is using emergency funding to respond to the threats associated with growing outbreaks of exotic fruit flies and New World screwworm. U.S. Secretary of Agriculture Tom Vilsack approved the transfer of $213.3 million from the Commodity Credit Corporation to APHIS to directly support emergency response efforts domestically and internationally to protect fruit, vegetable and livestock industries and producers.

      "Increasing our response efforts to exotic fruit fly and New World screwworm outbreaks is critical to minimizing their potential impact on our nation’s agriculture and trade," said USDA Under Secretary for Marketing and Regulatory Programs Jenny Lester Moffitt. "This funding will enable us to swiftly prevent both populations’ further spread before they become established and harder to eradicate."

  • APHIS History Highlights: APHIS and Mexico Take On Deadly Screwworm

    • Apr 12, 2022
    • USDA. Animal and Plant Health Inspection Service.

    • In the early 1970s, USDA's progress in eradicating screwworm—among the deadliest and most vicious of livestock pests—was at a crossroads. Department scientists had revolutionized the country's battle against the insect by creating a new technology. The concept was simple yet profound: rear and aerially distribute masses of sterile screwworm flies in infested areas, so the resident fly populations would have increasing difficulty reproducing—and eventually breed themselves out of existence. The new approach worked so well that by 1966, USDA declared screwworm eradicated within U.S. borders.

  • A New World Screwworm - A Story Map

    • USDA. Animal and Plant Health Inspection Service.

    • An interactive story map of the USDA's history of eradicating the infestation and the continuing efforts to keep screwworm out of the U.S.
      See also: APHIS in Action to explore plant and animal health or wildlife damage management data and Interactive Story Maps


Selected Resources

The section below contains highly relevant resources for this species, organized by source.

Federal Government
  • Livestock and Poultry Disease - New World Screwworm

  • Screwworm Eradication Program Records

    • USDA. ARS. National Agricultural Library.

    • The Screwworm Eradication Program Records, housed in Special Collections of the National Agricultural Library (NAL), documents one of the greatest success stories in the history of American agriculture. Led by the United States Department of Agriculture (USDA), the eradication of the screwworm from the United States, Mexico, and most of Central America marked a major victory over the destruction of domestic and wild animals by an insect which feeds only on the living tissue of warm-blooded animals.

      The Screwworm Eradication Program Records document research and eradication efforts from the 1930s through 2000. These materials include correspondence, plans, reports, scientific papers and manuscripts, publications, raw research data and research analyses, livestock producer information materials and reports, cooperative agreements, photographs, maps and artifacts.

State and Local Government