These flies are not like their relatives that feed on dead and decaying animals. No, the flesh-eating worms of these parasitic insects prefer to eat live animals such as cows, horses and pigs, and they can be deadly.
Another case of New World screwworm was recently stopped from entering the United States at a quarantine facility in Florida.
And humans are not immune. One traveler returned to the United States from Central America last summer carrying the parasite.
Maggots enter through open wounds and mucous membranes. They dig, or screw, into the flesh of an animal using “sharp mouth hooks,” according to the Animal and Plant Health Inspection Service. That’s how the New World screwworm got its name.
Is the New World screwworm in the United States? How close is it to Ohio? Here’s what you need to know.
A tusklike mandible that protrudes from the mouth of the larva of the screw rasp the flesh of warm-blooded animals. A wound may contain hundreds of such larvae.
‘Critical threat’ to US agriculture: How the USDA is preparing for the New World screwworm
New World screwworm case found at Florida facility
According to the Florida Department of Agriculture and Consumer Services, earlier this month screwworm larvae were found on a horse imported from Argentina undergoing a routine and required examination at a US Department of Agriculture approved import facility in South Florida.
There was no detection of NWS larvae outside the quarantine facility. The affected horse was treated, and out of an abundance of caution, the agency said in a statement that all cohort horses at the facility were also examined and treated.
“There is no detection of New World Screwworm in any Florida animal. The detection at the USDA import facility was handled professionally and according to existing protocols to ensure that the United States remains free of this devastating pest,” said Dr. Michael Short, state veterinarian, in the statement.
The infected horse had to remain in quarantine until it was re-examined and found free of parasites.
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Is the New World screwworm in the US or Ohio?
The insect was eradicated in the United States in the 1960s, in Mexico in the 1970s, and much of Central America by the early 2000s, according to the Centers for Disease Control and Prevention, USA TODAY reported.
However, the CDC said that new cases were reported in October 2024 in Panama, Costa Rica, Nicaragua, and Honduras. From there, it spread north, sparking fears that the insects would spread north into the United States. Their movement led the United States to block imports of live cattle, horses, and bison through southern border ports, reports USA TODAY.
ScienceAlert.com reported that in January 2026 there were 601 cases of active animals throughout Mexico, with eight in Tamaulipas – a state bordering Texas.
According to the USDA’s Animal and Plant Health Inspection Service, the New World screwworm is not currently present in the United States
The closest it has come to Ohio is a single human case in Maryland from a traveler returning from El Salvador in 2025.
What is so dangerous about the flight of the New World screwworm?
NWS flies are the size of a common housefly and lay eggs “on open wounds or other open body parts in live, warm-blooded animals,” according to the CDC. A wound as small as a tick bite can attract flies.
The eggs hatch and the maggots burrow into the wound to feed on the raw flesh, the CDC says. As you might expect, worms that dig into living things are very painful.
After eating, the larvae fall to the ground and burrow into it. They later emerge as adult screw flies, the CDC says.
New World screwworms in humans – what are the symptoms?
NWS infestations are very painful, according to the USDA. If you have an infestation, you may see worms around or in an open wound, or in your nose, eyes or mouth. Symptoms may include:
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Unexplained skin lesions (sores or sores) that do not heal.
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Skin sores or sores that get worse over time.
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Skin sores or painful sores.
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Bleeding from open wounds.
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You feel larval movement in a wound or pain in the skin, nose, mouth, or eyes.
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Seeing worms around or in open wounds.
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Foul odor from the site of infestation.
A sterile male screw fly marked with a numbered tag to study fly dispersal, behavior and longevity.
The United States plans to prevent the spread of the screw
The USDA plan to prevent the spread of screwworm includes investments of up to $100 million for innovations to find new ways to fight the insect and $750 million to create a facility in South Texas to sterilize flies and fight the spread, USA TODAY reported in September 2025.
Releasing sterile flies to disrupt the reproduction of the worm was a technique used to eradicate plague in the 1960s. The hope is that those sterile flies will then mate with wild ones, producing infertile eggs, experts said.
Another $21 million is being invested to renovate an existing fruit fly production facility in Metapa, Mexico, to produce more sterile flies.
This article originally appeared on The Columbus Dispatch: Flesh-eating parasites target the United States. Is Ohio safe? More about New World screwworm