New World Screwworm: Staff and Volunteer Training Guide
Recognizing and Responding to New World Screwworm
For comprehensive guidance, please view all resources on our Screwworm resource page, including:
You don't need to be a veterinarian to play a critical role in protecting the animals in your shelter. You just need to know what to look for and what to do when you see it.
Part 1: Background
New World Screwworm (Cochliomyia hominivorax) is a fly whose larvae burrow into the living tissue of animals through open wounds or moist body openings. Unlike most flies, these larvae feed on healthy tissue and cause damage that can worsen rapidly.
The pest was eliminated from the U.S. in 1966 but was confirmed in South Texas on June 3, 2026. While southern U.S. state shelters face the highest immediate risk, the fly's seasonal range can extend as far north as Canada. The AVMA has confirmed that travel makes it possible for NWS to be introduced into any U.S. state. Shelters receiving transfer animals from the South should also be on alert.
The good news: it is treatable when caught early. Your eyes and hands are one of the most powerful tools your shelter has right now.
Part 2: What You're Looking For
During your daily interactions with animals, watch and feel for any of the following:
Signs a wound may be infested:
- The wound looks bigger than it did yesterday
- There is a foul or unusual smell
- You see bloody or unusual drainage
- The animal seems to be in more pain than expected or is unusually restless
- The animal is shaking its head or licking obsessively at a spot
- You see small, pale larvae (maggots) moving in or near a wound
Wound types that are highest risk:
- Surgical incisions (including spay/neuter wounds)
- Bite wounds or puncture wounds
- Hot spots
- Ear wounds or infections
- Tick attachment sites
- Draining skin lesions
- Any open or moist wound
Part 3: What to Do If You Find Something
- Stay calm. Finding a suspected case is not a crisis if you act quickly.
- Do not touch or remove larvae. Leave the wound as-is until a vet or vet tech can assess it.
- Isolate the animal. Move it away from other animals immediately. Use gloves.
- Report it right away. Tell your supervisor and shelter veterinarian as soon as possible. Do not wait until end of shift.
- Document what you saw. Note the animal's ID, wound location and appearance, and when you noticed the change. Take a photo if your shelter's protocols allow.
- Follow your shelter's screwworm SOP. If you're not sure where it is, ask your supervisor now, before you need it.
Note: if a case is confirmed, USDA-APHIS protocol requires the animal to be placed under a hold order and supervised by a USDA-accredited or state veterinarian until treatment is complete and the animal is declared free of infestation.
Part 4: Daily Prevention Habits
- Do a hands-on wound check during every feeding or cleaning round. Look at surgical sites, ears, and anywhere that could collect moisture.
- Report any new or changing wounds to your supervisor immediately, even if you're not sure it's significant.
- Keep wounds covered and dry when practical. If a bandage is wet, dirty, or has come loose, report it.
- Never move an animal with an open wound to an outdoor or open-air area without checking with a vet or supervisor first.
- If you are handling intakes from Mexico, high-risk communities, or animals with unknown history, give wound checks extra attention.
Part 5: Intake Screening
When checking in a new animal, look for these on the intake form or ask directly:
- Has this animal been in Mexico or near the border recently?
- Are there any known wounds or injuries?
- Has the animal been treated for maggots or wound infestation?
- Has this animal been transported from Texas, New Mexico, or anywhere in the South recently?
Do a head-to-tail visual inspection on every intake. If you see anything concerning, flag it before the animal is housed with other animals.
Part 6: Protecting Yourself
New World Screwworm primarily affects warm-blooded animals, not humans, but good hygiene matters. Wash your hands thoroughly after handling any animal with wounds. Wear gloves when examining wounds or handling wound dressings.
Quick Reference
Report immediately if you see: enlarging or foul-smelling wound, bloody drainage, visible larvae, unusual pain or restlessness, head shaking or obsessive licking.
Always: Report to supervisor and vet right away. Document what you saw. Follow your shelter’s current SOP.
Never: Never remove larvae yourself. Do not wait until the end of shift to report. Never move a suspected animal to outdoor housing without vet or staff leadership approval.