These flies do not feed on dead and decaying animals like their relatives. No, the flesh-eating maggots of these parasitic insects prefer to feed on live animals such as cattle, horses and pigs, and they can be deadly.
Recently, a quarantine facility in Florida prevented another case of New World screwworm from entering the United States.
Humans are not immune. Last summer, a traveler returned to the United States from Central America with the parasite.
Maggots enter through open wounds and mucous membranes. They use “sharp mouth hooks” to burrow or twist into the animal’s flesh, according to the Animal and Plant Health Inspection Service. This is how New World screwworms get their name.
Is New World Screwworm in the United States? How close is it to Ohio? Here’s what to know.
Screwworm larvae have fang-like mandibles protruding from their mouths to chew the flesh of living blood-blooded animals. A single wound may contain hundreds of these larvae.
US agriculture faces ‘serious threat’: How the USDA is preparing for New World screwworm
New World screwworm cases found at Florida factory
Earlier this month, screwworm larvae were found in a horse imported from Argentina during a routine and required inspection at a USDA-approved import facility in South Florida, according to the Florida Department of Agriculture and Consumer Services.
No NWS larvae were found outside quarantine facilities. The affected horses were treated and all horses at the facility are examined and treated out of an abundance of caution, the agency said in a statement.
“New World screwworm has not been detected in any animals in Florida. Testing at USDA import facilities is done professionally and in accordance with existing protocols to keep the United States safe from this devastating pest,” state veterinarian Dr. Michael Short said in the statement.
Infected horses will remain in isolation until re-examined and found to be free of parasites.
Human screwworm: Deadly bovine screwworm parasite found in US patient. what to know
Is New World screwworm in the United States or Ohio?
The insect was eradicated from the United States in the 1960s, Mexico in the 1970s and much of Central America in the early 2000s, according to the Centers for Disease Control and Prevention, USA Today reported.
However, Panama, Costa Rica, Nicaragua and Honduras reported new cases in October 2024, the CDC said. From there, it spread northward, raising concerns about the insect spreading north into the United States. Their actions led to the U.S. banning the import of live cattle, horses and bison through southern border ports, USA Today reported.
ScienceAlert.com reported that in January 2026, there were 601 animal cases across Mexico, eight of which occurred in the state of Tamaulipas, which borders Texas.
New World screwworms are not currently present in the United States, according to the USDA Animal and Plant Health Inspection Service
The closest case to Ohio is a case in Maryland infected by a traveler who returned from El Salvador in 2025.
What are the dangers of New World screwworm flies?
NWS flies are the same size as common house flies and they lay their eggs in “open wounds or other open parts of the body of living warm-blooded animals,” according to the Centers for Disease Control and Prevention. A wound as small as a tick bite can attract flies.
The eggs hatch and the maggots burrow into the wound and feed on live flesh, the CDC said. As you might expect, maggots burrowing inside living things are extremely painful.
After feeding, the larvae drop to the ground and burrow into it. They later emerge as adult screwworm flies, the CDC says.
New World screwworm infection in humans – what are the symptoms?
According to the USDA, NWS infections are very painful. If you have a maggot infection, you may see maggots around or in open wounds, or in your nose, eyes, or mouth. Symptoms may include:
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Unexplained skin injury (wound or sore) that does not heal.
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Skin wounds or ulcers get worse over time.
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Painful skin cuts or ulcers.
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Open sores that bleed.
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Feel the larvae moving in cuts or sores on your skin, in your nose, mouth, or eyes.
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Maggots are seen around sores or in open sores.
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A foul odor emanates from the infected area.
Sterile male screwworm flies are numbered and tagged for use in studying fly dispersal, behavior and lifespan.
U.S. plan to prevent the spread of screwworm
USA Today reported in September 2025 that the USDA’s plan to prevent the spread of screwworm flies includes investing up to $100 million in innovation to find new ways to combat the insect, and investing $750 million to build a facility in South Texas to sterilize the flies and curb the spread.
Releasing sterile flies to disrupt screwworm reproduction was a technique used to eradicate this pest in the 1960s. Experts say they hope these sterile fruit flies will mate with wild fruit flies and lay sterile eggs.
An additional $21 million has been invested to renovate existing fruit fly production facilities in Metapa, Mexico, to produce more sterile fruit flies.
This article originally appeared in The Columbus Dispatch: Flesh-eating parasite targeting U.S. Is Ohio safe? More information about New World screwworms