New World screwworm (NWS), or Cochliomyia hominivorax, is a species of parasitic fly whose larvae (maggots) feed on the living tissue or flesh of people and warm-blooded animals. NWS flies are attracted to open wounds and body openings like the nose, eyes, ears, and mouth, where they lay eggs. When the eggs hatch, the larvae burrow or "screw" into the tissue causing a rapidly worsening, often painful and foul-smelling wound. There is currently no medication labeled to treat an NWS infestation in humans. The larvae must be removed by a healthcare professional (for humans) or by a veterinarian for animals.
| Image: Two C. hominivorax larvae, CDC. |
NWS flies are normally found in South American and Caribbean countries. NWS flies were Once eradicated from the U.S., Mexico, and most of Central America in the 1960s using a method called the sterile insect technique. However, NWS flies have the fly has been resurging in these areas since 2023. NWS was first detected in Mexico in 2024 and first detected in the US in Texas in June 2026.
There are no human cases of NWS infestation in Indiana.
Listen to "The Doctor is IN" podcast from the Indiana Department of Health
Indiana Department of Health's Senior Medical Entomologist Lee Green and State Public Health Veterinarian Dr. Jen Brown explain how NWS can impact humans and what clinicians should keep in mind about this serious pest even though the risk is low.
When New World screwworm (NWS) larvae (maggots) infest humans or animals, they cause a severe parasitic condition called myiasis. Signs and symptoms can include
- Feeling larvae move or seeing maggots within a skin wound or sore, or in the ears, nose, eyes, or mouth or other body openings.
- Painful skin wounds or sores that quickly worsen (within a day or two).
- A foul-smelling odor from the site of the infestation.
- Bleeding from open sores.
Bacteria can also infect wounds where NWS larvae are present and may cause infection that can lead to symptoms like fever or chills.
People who suspect that they may have a case of New World screwworm (NWS) infestation should immediately seek medical attention.
New World screwworm infestations begin when a female fly lays eggs on open wounds or other parts of the body in live, warm-blooded animals. The smell of a wound or body opening such as the nose, mouth, eyes, ears, or genitals can attract female flies. Wounds as small as a tick bite may attract a female fly to lay her eggs. One female can lay 200–300 eggs at a time and may lay up to 3,000 eggs during her 10- to 30-day lifespan.
Eggs hatch into larvae that burrow into the wound to feed on the living flesh. After feeding for about 7 days, the larvae drop to the ground, burrow into the soil, and later emerge as adult screwworm flies.
NWS myiasis cannot be directly spread from an infested animal or person. However, eggs may be laid by adult flies on different people living in the same space, which can lead to infestation.
Adult female Cochliomyia hominivorax flies lay clusters of eggs near open wounds (e.g., the umbilicus of newborns) or on mucous membranes inside the nose, mouth, ears, eyes, or genitals . The eggs hatch into first-instar larvae (maggots), which burrow into the body and feed on the living tissue, leading to rapid expansion of wounds . The larvae grow through a process known as molting, developing into second- and third-instar larvae (maggots) over a period of approximately 7 days, after which they drop from the host and enter a new life stage (pupae) in the upper layers of the soil . The adult fly emerges from the pupa after 7 – 54 days depending on temperature and humidity  . The adult female fly mates with a male only once and then may lay up to 3,000 eggs within her 10 to 30-day lifespan. |
People may be at increased risk for NWS in areas where the flies are present if they:
- Spend a lot of time outdoors during the day, especially if sleeping or unable to keep flies away.
- Have any open wounds. Even small breaks in the skin, including from a scratch, insect bite, or recent surgery may attract NWS flies.
- Have a medical condition that can cause bleeding or open sores, such as from skin or sinus cancer, or from treatments that create breaks in the skin.
- Live, work, or spend an extended amount of time with (or near) livestock or other warm-blooded animals.
Preventing breaks in the skin and avoiding NWS flies is key to protecting yourself in areas where the flies are present.
- Keep open wounds clean and covered, no matter the size or location on the body.
- Sleep indoors with closed windows or screened open windows. If you are outside, sleep under a bed net or inside a screened tent.
- Protect your skin and prevent insect bites by
- Using an EPA-registered insect repellent.
- Treating clothing and gear with products containing 0.5% permethrin.
- Wearing loose-fitting, long-sleeved shirts and pants, hats, and socks to limit access to your body by NWS flies and biting insects.
New World screwworm: What You Need to Know (English | Spanish)
Factsheet on NWS identification for providers of homeless services
Healthcare providers caring for people with suspected cases of NWS infestation should immediately contact the Indiana Department of Health (IDOH) at 317-233-1325.
NWS Recommendations for Healthcare Providers (CDC)
COCA Call: Resurgence of New World Screwworm in the Americas: What Healthcare Providers Need to Know
Page last reviewed/updated: June 2026
