Screwworm in Cattle: What Every Rancher Needs to Know: Summer 2026
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If you raise cattle in Texas or anywhere across the southern United States, screwworm in cattle is a threat that has returned with urgency this summer. On June 3, 2026, the USDA confirmed the detection of New World screwworm (NWS) larvae in the umbilical area of a calf in southern Texas — the parasite's return to U.S. soil for the first time since 1966. 1 This development has put ranchers, veterinarians, and federal agencies on high alert.
Understanding what this parasite is, how it spreads, what warning signs to watch for, and how to protect your herd through proper wound management is not just good practice — this summer, it could mean the difference between a manageable situation and a devastating loss. This guide provides clear, science-backed information for cattle ranchers and livestock owners, and explains the role effective products like Vetericyn Plus® Antimicrobial Livestock Gel, Livestock Spray, and All Animal Wound Care — as well as Vetericyn Super 7® Ultra Navel Care, a critical tool for protecting the most vulnerable entry point on newborn calves — play in keeping your animals safe this season.
In this article...
What Is New World Screwworm?
The New World screwworm (Cochliomyia hominivorax) is a parasitic fly whose larvae feed exclusively on living tissue of warm-blooded animals — not dead or decaying matter. This is what makes it uniquely dangerous compared to other fly species. 2
According to the American Veterinary Medical Association (AVMA), adult screwworm flies are similar in size to a common housefly, with orange eyes, a metallic blue or green body, and three dark stripes along their backs. 2 The female fly is attracted to any open wound, body orifice, or fresh umbilical cord — a critical detail for ranchers managing newborn calves. She lays eggs at the wound's edge, which hatch within hours.
Once hatched, the larvae use their sharp mouth hooks to burrow deeply into the tissue. According to the AVMA, by three days after initial infestation, hundreds or even thousands of larvae may be present. 2 The wound grows larger and deeper, attracting more flies and more eggs in a destructive cycle. Without veterinary intervention, an infested animal can die within days to weeks.
Common wound sites that attract screwworm flies include:
- Fresh branding, dehorning, or castration sites
- Calving injuries and the umbilical cords of newborn calves
- Tick bites and barbed wire abrasions
- Body orifices such as the nose, ears, eyes, and genitalia
The Summer 2026 Texas Outbreak: Why This Matters
The Texas Animal Health Commission (TAHC) confirmed the return of screwworm in cattle to Texas on June 3, 2026 — the first occurrence since the U.S. eradicated the pest in 1966. 3 Since then, cases have been confirmed across an established NWS Infested Zone spanning 16 counties, including Coke, Crockett, Edwards, Gillespie, Kerr, Kimble, La Salle, Pecos, Schleicher, Sutton, Terrell, Tom Green, Uvalde, Val Verde, Webb, and Zavala.
All warm-blooded animals in these zones — livestock and pets alike — are prohibited from moving outside the quarantine area without prior authorization from TAHC. 3 This represents a significant operational disruption for ranchers already managing one of the most challenging livestock environments in recent memory.
Texas is home to approximately 12.5 million head of cattle — roughly 14% of the entire U.S. herd, more than twice as many as Nebraska, the next largest cattle state. 4 The American Farm Bureau Federation has estimated that an outbreak comparable to the 1976 incident, adjusted for today's cattle inventory, could cost the Texas livestock industry an estimated $1.9 billion annually. 4
NWS does not spread directly from animal to animal. Instead, as the USDA explains, female flies deposit eggs in open wounds or body openings, and every infestation is a potential source of many more flies. 1 This makes rapid recognition, reporting, and wound management central to controlling spread.
How to Identify Screwworm in Your Herd
Early detection is critical. The AVMA identifies the following signs of NWS myiasis that every rancher should know: 2
Signs in Wounds
- Larvae visible in wounds or body orifices (nose, ears, genitalia, umbilicus)
- Egg masses in or around wounds
- Wounds with serosanguinous discharge and a foul odor of decay
- Wounds that enlarge or deepen over time rather than healing
Behavioral Signs in Cattle
- Behavioral signs of irritation, such as head shaking or rubbing against structures
- Signs of pain — depression, irritability, or reduced appetite
- Animals isolating from the herd
- Newborn calves showing discomfort around the navel area
The AVMA notes that NWS larvae are distinct from other fly larvae: they feed on healthy, living tissue and burrow deeply, causing rapidly enlarging wounds. In deep or narrow wounds, subtle movement may be the only visible sign. 2 This distinguishes them from other maggot species that remain at a wound's surface. If you find a maggot and need to determine whether it is reportable, knowing what NWS larvae look like is critical. According to Texas Tech University School of Veterinary Medicine, New World screwworm larvae are a traditional white to cream color with a tapered body, surrounded by black spines arranged in a spiral fashion, and two dark vertical slits on the back. 8 These features set them apart from non-reportable fly species and should prompt immediate contact with your veterinarian or TAHC.
If you suspect an infestation, contact your state animal health official or the TAHC Veterinarian on Call immediately at 1-800-550-8242. NWS is reportable in Texas and must be reported within 24 hours of suspicion. 3
Prevention: Your First and Best Defense
The USDA and extension specialists consistently emphasize that prevention is the foundation of any effective management strategy. The TAHC recommends that livestock and pet owners stay vigilant, monitor animals regularly, and report any suspicions immediately. 3
Schedule High-Risk Procedures During Low-Risk Periods
Texas A&M AgriLife Extension recommends shifting wound-producing procedures — branding, castration, dehorning, and calving — to winter months when screwworm fly activity is at its lowest. 5 Aligning livestock management practices with seasonal risk patterns is one of the most effective tools available to producers.
Treat Navels and Wounds Immediately — Every Time
The USDA APHIS recommends treating umbilical cords of all newborn animals and all wounds without delay. 6 On the navel side, this means applying Vetericyn Super 7® Ultra Navel Care within 30 minutes of birth while the cord is still wet — rapidly drying the umbilical stump and closing what is the most vulnerable entry point for screwworm flies on a newborn calf. On the wound care side, every break in the skin across your operation — a tick bite, a barbed wire scratch, a post-castration site — must be addressed just as promptly. Vetericyn Plus® Antimicrobial Wound Care products help clean and support healing for these everyday injuries before they become infestation opportunities. Together, navel care and wound care form the front line of your daily screwworm defense.
Increase Herd Surveillance
More frequent inspections mean faster detection. Texas A&M AgriLife Extension specifically highlights diligent surveillance and rapid response protocols as pillars of an effective NWS management plan. 5 Inspect body openings — nose, ears, eyes, genitalia — as well as any wound sites during every herd check.
Handle Livestock Carefully
The USDA advises ranchers to inspect pens and equipment for sharp objects that can cause wounds, and to handle livestock with care to minimize injury. 6 Fewer wounds mean fewer infestation opportunities.
Navel Dipping: Protecting Your Most Vulnerable Calves
Of all the entry points the New World screwworm fly targets, the freshly severed umbilical cord of a newborn calf is among the most significant. Moist, exposed, and open for several days after birth, it is exactly the kind of site female screwworm flies seek out. Treating the navel immediately — ideally within 30 minutes of birth — is one of the most impactful steps a rancher can take during the current outbreak.
Vetericyn Super 7® Ultra Navel Care is a fast-acting umbilical cord dry-out solution developed specifically for production livestock. Proven up to 30% faster than 7% tincture of iodine at drying umbilical tissue, it is non-toxic, non-corrosive, and iodine-free — safer for animals and for the people applying it. The dyed formula leaves a visible orange marker confirming the navel has been treated, which is especially useful in high-volume calving operations. Apply using a teat dip cup: submerge the cord fully, gently press the cup against the abdomen, use one dose per calf, and reapply after 12 hours in dirty environments. Make navel dipping the first thing that happens after every calf hits the ground.
Wound Management Across Your Operation: Vetericyn Plus®
Every wound across your operation — from routine husbandry to calving injuries to environmental abrasions — represents a potential screwworm entry point during this summer's elevated fly pressure. The AVMA's recommended response protocol for any NWS case includes wound care with antiseptics to prevent secondary infections. 2 The same principle applies proactively: clean, well-managed wounds heal faster and attract fewer flies.
Vetericyn Plus® is the trusted umbrella for keeping your entire operation protected. Formulated with hypochlorous acid (HOCl) technology, Vetericyn Plus® products help clean wounds, support healthy tissue recovery, and create an inhospitable environment for secondary bacterial infection — all without stinging, burning, or requiring a prescription. The Vetericyn Plus® line includes:
- Vetericyn Plus® Antimicrobial Livestock Spray — quick, hands-free application for field conditions and everyday wound management across your herd
- Vetericyn Plus® Antimicrobial Livestock Gel — longer-contact coverage for deeper wounds or sites where you need the solution to stay in place
- Vetericyn Plus® All Animal Wound Care — extends the same HOCl-powered protection to every warm-blooded animal on your property, including horses, goats, sheep, hogs, and companion animals — all equally susceptible to screwworm infestation
Together, these products give you a complete Vetericyn Plus® toolkit from the delivery pen to the pasture. Note: Vetericyn Plus® products do not treat or prevent screwworm infestation directly — that requires FDA-authorized antiparasitic treatments prescribed by a veterinarian. However, keeping wounds clean and healing quickly is a foundational layer of any integrated screwworm protection strategy.
If You Suspect an Infestation: Step-by-Step
The AVMA outlines the following protocol for any suspected NWS case: 2
1. Isolate the animal immediately from the rest of the herd
2. Contact your state animal health official and USDA-APHIS area veterinarian. After-hours reporting line: (866) 536-7593
3. If directed to do so: collect larvae from several wound sites using disposable gloves and forceps, place in a vial of 70% alcohol, and submit to the National Veterinary Services Laboratories with a completed Parasite Submission Form
4. Do not move the animal off your premises until given authorization by a USDA-accredited or official veterinarian confirming the animal is free of screwworm
5. Reexamine the animal 24 hours after treatment to confirm no live larvae remain; retreat if necessary
6. Monitor your premises weekly for a full month after the affected animal is released
Report all suspected cases to TAHC within 24 hours at their regional office or the Veterinarian on Call: 1-800-550-8242.
Stay Informed. Stay Vigilant. Protect Your Herd This Summer.
The return of screwworm in cattle to Texas this summer is a serious development — but a manageable one. The U.S. has eradicated this pest before through coordinated effort, and the same tools and determination are being deployed again. Your role as a producer starts with knowledge: knowing what to look for, how to minimize wound-related risk, and when and how to report.
Make wound management and navel care a non-negotiable part of your daily operation this season. Dip every navel with Vetericyn Super 7® Ultra immediately at birth. Treat every wound promptly with Vetericyn Plus® Antimicrobial products. Schedule high-risk procedures during lower-risk months. And keep your veterinarian's number — and TAHC's — close at hand.
For real-time case maps, quarantine zone updates, and official guidance, visit Screwworm.gov, TAHC's NWS page, and AVMA's NWS resource hub.
Frequently Asked Questions
1. How do I know if my cattle have screwworm?
Watch for wounds that are growing larger, draining, or emitting a foul odor. Examine the wound for egg masses along the edges or larvae burrowing into the tissue. The AVMA notes that by day three, hundreds or thousands of larvae may be present — act at the first sign of any unusual wound. 2 Infested animals often isolate from the herd and show signs of pain or irritability.
2. Why is the navel so important for screwworm prevention in calves?
The freshly severed umbilical cord is one of the most vulnerable screwworm entry points on a newborn calf. It remains moist and exposed for several days after birth, attracting egg-laying flies. Dipping the navel with Vetericyn Super 7® Ultra Navel Care within 30 minutes of birth accelerates cord dry-down and significantly reduces this window of vulnerability — making it one of the single most effective steps a rancher can take.
3. Can screwworm spread from animal to animal?
No — screwworm does not spread directly between animals. According to USDA APHIS, female flies deposit eggs in open wounds of living hosts. 1 The risk to your herd comes from fly pressure in your area and the presence of unmanaged wounds — not direct animal-to-animal contact.
4. Is beef from a screwworm-affected area safe to eat?
Yes. USDA has confirmed the U.S. food supply is safe. NWS larvae do not infest meat, fruits, vegetables, or other food products. 1 Screwworm is a livestock production and animal welfare concern — not a food safety issue.
5. What should I do if I live in a quarantine zone?
Follow all TAHC Executive Director Orders for your county. Do not move warm-blooded animals out of the zone without prior TAHC authorization and a valid NWS Treatment/Movement Certificate. 3 For real-time quarantine zone maps and county-by-county updates, visit tahc.texas.gov/emergency/nws.html and screwworm.gov.
Sources
1. U.S. Department of Agriculture Animal and Plant Health Inspection Service. "USDA Confirms Presence of New World Screwworm in the United States." USDA APHIS, 3 June 2026, www.aphis.usda.gov/news/agency-announcements/usda-confirms-presence-new-world-screwworm-united-states.
2. American Veterinary Medical Association. "New World Screwworm (NWS)." AVMA, www.avma.org/resources-tools/one-health/veterinarians-and-public-health/new-world-screwworm. Accessed 24 June 2026.
3. Texas Animal Health Commission. "New World Screwworms." TAHC, www.tahc.texas.gov/emergency/nws.html. Accessed 24 June 2026.
4. American Farm Bureau Federation. "New World Screwworm Moves Beyond Containment Threshold." Market Intel, American Farm Bureau Federation, 22 May 2025, www.fb.org/market-intel/new-world-screwworm-moves-beyond-containment-threshold.
5. Texas A&M AgriLife Extension Service. "Rethinking Livestock Management to Consider Screwworm." Texas A&M AgriLife Extension Service, agrilifeextension.tamu.edu/rethinking-livestock-management-to-consider-screwworm/. Accessed 24 June 2026.
6. U.S. Department of Agriculture Animal and Plant Health Inspection Service. "New World Screwworm Prevention for Animals." USDA APHIS, www.aphis.usda.gov/livestock-poultry-disease/cattle/ticks/screwworm. Accessed 24 June 2026.
7. U.S. Food and Drug Administration Center for Veterinary Medicine. "New World Screwworm: Information for Veterinarians." FDA, 5 June 2026, www.fda.gov/animal-veterinary/safety-health/new-world-screwworm-information-veterinarians.
8. Texas Tech University School of Veterinary Medicine. "New World Screwworm Identification and Reporting." Texas Tech University School of Veterinary Medicine, www.ttuhsc.edu/medicine/veterinary. Accessed July 2026.
