New World Screwworm: What Every Cattle Producer Should Know
New World screwworm has become a major concern for livestock producers across Texas. While the parasite was eradicated from the United States decades ago, recent detections have reminded producers that early identification and quick action are critical to protecting individual herds and the cattle industry as a whole.
Whether you have a few head or a large commercial operation, knowing what to look for and what to do if you suspect screwworm can help prevent further spread.
What Is New World Screwworm?
New World screwworm is the larval stage of a fly that lays its eggs in open wounds or natural body openings of warm-blooded animals. Unlike many other maggots that feed on dead tissue, New World screwworm larvae feed on healthy, living tissue, causing wounds to become larger and more painful over time. If left untreated, infestations can become severe and even fatal.
Cattle are among the most commonly affected animals, but screwworm can also infest horses, sheep, goats, wildlife, pets, and, in rare cases, people.
How to Spot New World Screwworm
Early detection is one of the best tools producers have.
Watch for:
Wounds that continue getting larger instead of healing
Bloody or foul-smelling drainage
Maggots deep inside the wound
Animals constantly licking, biting, or rubbing an area
Swelling around a wound
Depression, reduced appetite, or weight loss in severe cases
Fresh wounds from branding, castration, dehorning, ear tagging, wire cuts, tick bites, or calving should all be monitored closely. Female screwworm flies are attracted to even small wounds.
What Do New World Screwworm Maggots Look Like?
New World screwworm larvae look different from the common maggots producers may occasionally see.
They are typically:
Creamy white in color
Cylindrical in shape with rings of small spines around each body segment
Found feeding head-first deep inside living tissue
Often clustered together in the wound
Unlike scavenger maggots that feed on dead tissue, screwworm larvae burrow deeper into healthy flesh, causing the wound to expand instead of heal. If you suspect the larvae may be New World screwworm, do not assume they are harmless. Report the case immediately.
What Should You Do If You Suspect Screwworm?
If you believe an animal may have New World screwworm:
Isolate the animal if possible.
Contact your veterinarian immediately.
Report the suspected case to the Texas Animal Health Commission.
Avoid moving the animal until you receive guidance from animal health officials.
Prompt reporting allows officials to confirm the diagnosis quickly and helps prevent the parasite from spreading to other livestock and wildlife.
What If You're Planning to Sell Cattle?
If you are planning to bring cattle to the sale barn and notice a suspicious wound or possible screwworm infestation, contact the sale barn before hauling the animals.
Selling or transporting cattle with a suspected screwworm infestation could increase the risk of spreading the parasite. The best course of action is to work with your veterinarian and state animal health officials to determine the proper next steps before moving the animals.
At Meridian Livestock Commission, protecting the health of all livestock coming through the barn is a top priority. If you have concerns about cattle you were planning to consign, give us a call. We'd much rather visit with you ahead of time and help point you in the right direction than risk exposing other livestock.
Tools and Resources Available to Producers
Fortunately, producers have several resources available to help identify, report, and manage New World screwworm.
Some of the best resources include:
USDA APHIS identification guides and updates
Texas A&M AgriLife Extension educational materials
Texas Animal Health Commission reporting information
Your local veterinarian
These organizations provide the latest recommendations, reporting procedures, and educational materials as the situation evolves.
Stay Vigilant
The recent detections serve as an important reminder that routine herd checks matter.
Taking time to inspect cattle, monitor wounds, and address concerns early can help protect your herd and the broader cattle industry.
If you notice something that doesn't look right, don't wait. Contact your veterinarian, report suspected cases, and reach out to Meridian Livestock Commission if you have questions about bringing cattle to the sale barn.
Working together is one of the best ways to protect the health of our livestock and the future of our industry.
Additional Resources
USDA APHIS – New World Screwworm Informationhttps://www.aphis.usda.gov/livestock-poultry-disease/cattle/ticks/screwworm
Texas A&M AgriLife Extension – New World Screwworm Resourceshttps://agrilifeextension.tamu.edu/new-world-screwworm/
Texas Animal Health Commission – New World Screwworm Informationhttps://www.tahc.texas.gov/emergency/nws.html
CDC – New World Screwworm Situation Summaryhttps://www.cdc.gov/new-world-screwworm/situation-summary/index.html