New World Screwworm: Fly Mitigation and Wound Management
A Layered Approach to New World Screwworm and Protecting Animals in Your Care
For comprehensive guidance, please view all resources on our Screwworm resource page, including:
Updated: June 30, 2026
With New World Screwworm confirmed in South Texas, shelters in southern states should approach fly mitigation in layers. The core risk is a female fly finding an open wound or moist body opening. The good news: there are simple strategies to prevent pets from being affected, and reducing the opportunity at every level is what keeps your animals safe.
New World Screwworm (NWS) is a parasitic fly whose larvae burrow into body openings of living animals including wounds, surgical incisions, exposed navels of newborn pets and sometimes orifices. They are highly treatable when caught early but can progress quickly and cause damage or even death if left untreated.
The six areas below are your priorities. Start with wound management; it has the highest impact.
1. Aggressive Wound Management (Start Here)
Conduct daily hands-on wound checks for every animal. Keep all wounds clean, dry, and covered whenever possible.
- Prioritize daily monitoring for any animal with:
- Surgical incisions
- Bite wounds or hot spots
- Draining abscesses
- Ear injuries
- Skin infections
- Tick attachment wounds
Consider prioritizing daily monitoring for post-surgical animals, recent spay/neuter patients, puppies and kittens, seniors, and animals with skin disease or trauma recovery needs. Pets who receive appropriate preventatives face very low risk.
Expanding access to effective parasiticides in shelters and rescues is a simple, high-impact strategy. These products may help reduce the risk of NWS infestation and are available for treatment of affected animals under current FDA approvals, conditional approvals, or emergency authorizations. For more information on medications per species, see the NWS Need to Know resource.
2. Move High-Risk Animals Indoors
If your facility has any open-air housing, these animals should be your priority for indoor placement:
- Post-surgical and recent spay/neuter patients
- Neonatal kittens and puppies
- Senior pets
- Pets recovering from trauma or with skin conditions
3. Physical Fly Exclusion
For open-air or partially open spaces:
- Increase airflow with fans (flies avoid high-airflow areas)
- Install fine insect screening around recovery kennels
- Add screened shade structures
- Use fly curtains at kennel entrances
- Consider portable screened kennel pods for animals that need extra protection
4. Develop a Suspect Case Protocol
Every shelter near confirmed cases should have a written procedure before a case arrives. When suspicious larvae are found:
- Isolate the animal immediately.
- Photograph the wound.
- Contact your shelter veterinarian.
- Per USDA-APHIS protocol, any animal with a suspected or confirmed case must remain under the supervision of a USDA-accredited or state/federal veterinarian until screwworm is confirmed, treatment is complete, and the animal is declared free of infestation. Euthanasia of an animal does not kill larvae. Carcasses must be frozen or incinerated. Burial alone will not prevent further infestation. Treating the host animal with FDA-approved medications is the most effective way to kill the larvae.
- Administer medication per your vet's guidance. Check the FDA's current list of approved and emergency-authorized products.
- Notify your State Animal Health Official.
- Contact USDA APHIS. After-hours emergency line: (866) 536-7593.
- Preserve larvae samples if instructed.
- Document the animal's origin and movement history.
Having this written down and practiced in advance means your team doesn't have to figure it out in the moment.
5. Intake Screening
Add a visual wound inspection to every intake. Consider adding the following questions to your intake form for animals coming from high-risk areas:
Has this animal:
- Traveled from Mexico or recently crossed the border?
- Been imported or found near a port of entry?
- Had recent wounds or been treated for maggots?
- Been transported from Texas, New Mexico, or a southern state?
6. Daily Surveillance
Train all staff and volunteers to report the following immediately, rather than waiting for the next vet check:
- Enlarging or foul-smelling wounds
- Bloody wound drainage
- Unexplained pain or restlessness
- Head shaking or excessive licking
- Visible larvae
The earlier a potential case is caught, the better the outcome for the animal. Early detection is the difference between a treatable situation and a life-threatening one.