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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


  • 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.

  • ARS Science Key to Stopping ‘Man-Eating’ Parasite

    • Jan 4, 2021
    • USDA. ARS. Tellus.

    • Eliminating screwworms from the United States saves farmers and ranchers nearly $900 million in lost livestock each year.

  • USDA Agencies Work Together to Eradicate an Old Foe: the Screwworm

    • Jan 9, 2018
    • USDA. Blog.

    • Early in October 2016, the U.S. Department of Agriculture (USDA) was faced once again with New World screwworm, which had been eradicated from the United States more than three decades ago. Infestation of this flesh-eating parasite was confirmed in deer from the National Key Deer Refuge in the Florida Keys.

      USDA’s Animal and Plant Health Inspection Service (APHIS) immediately began releasing sterile male flies in Florida’s affected areas as part of an aggressive eradication campaign. By March 2017, the screwworm had been successfully eradicated from Florida.

  • A New World Screwworm - A Story Map by USDA

    • 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 Interactive Maps to explore plant and animal health or wildlife damage management data and an index of APHIS Maps


Selected Resources

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

Federal Government
  • Emergency Management - New World Screwworm

    • USDA. Animal and Plant Health Inspection Service.

  • 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