A new pest called screwworm has been making headlines across the U.S. for the past two months. Here’s what you need to know.
What is screwworm? New World screwworm (NWS, Cochliomyia hominivorax) is a serious pest that affects livestock, pets, wildlife, and, less commonly, people and birds.
Adult screwworm flies are about the size of a common housefly or slightly larger. Their larvae feed on the living tissue of warm-blooded animals.
The USDA confirmed the first case of NWS on June 3, 2026.
How many cases are there? Central American countries and Mexico have reported more than 189,000 cases in animals and 2,274 cases in people.
There have been no reports of locally acquired human infections with NWS in the U.S.
As of July 14, the USDA Animal and Plant Health Inspection Service (APHIS) reported 37 domestically acquired animal cases of NWS in the U.S.
Where is screwworm? Screwworm has been reported in Zavala, La Salle and Gillespie counties in Texas, as well as Lea County, New Mexico.
Am I at risk? According to the Centers for Disease Control and Prevention (CDC), the current risk to the public and animals in the U.S. is very low.
In areas where NWS flies are present, the best way to protect yourself from infestation is to:
- Keep open wounds clean and covered, no matter how small or where they are located on the body.
- Wear loose-fitting, long-sleeved shirts and pants, hats, and socks to limit exposed skin.
- Use an EPA-registered insect repellent.
- Treat clothing and gear with products containing 0.5% permethrin.
- Sleep indoors or in rooms or tents with screens.
What are the symptoms? If you see or feel maggots (larvae) in or on a wound or other area of your body, contact your health care provider immediately. They will need to remove all of the maggots, sometimes through surgery. Do not try to remove or dispose of the maggots yourself.
Symptoms can include:
- Unexplained, painful wounds or sores that do not heal.
- A foul-smelling odor or bleeding from the site of the infestation.
- Seeing maggots or feeling movement in open wounds or sores or in areas of the body such as the nose, mouth, eyes, ears or genitals.
