The Return of a Livestock Nightmare: Screwworm Cases Confirmed

In 1933, the livestock industry faced a devastating enemy: the screwworm. Following a monumental eradication campaign, the parasite was officially declared eliminated in the 1960s—a historic victory for agriculture.

Unfortunately, that victory is being challenged. The threat is back.

Since June 3rd, authorities have already confirmed five active cases, proving this destructive pest has returned. The current toll (as of June 9th, 2026) includes three calves, one goat, and a domestic dog.

The Biology of a Flesh-Eating Threat

To protect your animals, it helps to understand how this parasite operates. The danger begins with the female New World screwworm fly, a specific type of blowfly. While the adult fly itself is harmless to livestock, its offspring are devastating.

Female flies are drawn to the warm, foul odors of open wounds or sensitive body openings—including the mouth, nose, ears, and genitals. Once she finds a host, she can lay up to 300 eggs at a time. Within just 24 hours, those eggs hatch into larvae: the actual screwworms.

These maggots get their name from their horrific feeding behavior. They burrow headfirst into live flesh, eating as they go, mimicking a screw being driven into wood.

What to Look For: Key Warning Signs

Identifying an infestation early can save your animal's life. When inspecting your livestock or pets, watch closely for these red flags:

• Unusual Wound Appearance: Look for wounds that appear to be expanding rather than healing, or holes in the skin that look pocketed or deeply tunneled.

• Distinctive Odor: Screwworm infestations produce a highly specific, foul, and pungent odor that attracts even more flies.

• Seeping Discharge: Watch for an abnormal amount of bloody or dark fluid leaking from a wound or body opening.

• Visible Larval Movement: If you look closely at the wound, you may see the tightly packed, screw-shaped maggots moving vertically as they feed.

• Behavioral Changes: Infected animals often become extremely restless, uncomfortable, or lethargic, and they may repeatedly scratch, bite, or lick at the site of the infestation.

A Deadly Timeline: Act Immediately

Time is your enemy. These flies do not discriminate; they can infect absolutely any living being, whether it is a cat, dog, horse, or cow. The speed of their destruction is terrifying—if left untreated, screwworms can take down a full-grown, healthy steer in as little as 7 to 14 days.

Because of this rapid timeline, we need to be keeping a close eye on all of our animals right now. Check your herds and pets daily. If you notice any signs of maggots or unusual wounds, immediately contact your veterinarian. Prompt veterinary care is critical to treat the infestation and prevent fatal secondary infections.

To stay prepared and protect your livestock or pets, ensure your barn is stocked with preventative treatments and fly spray. You can find robust topical protectants, first aid supplies, and pest repellents through the Teskey's Animal Care Collection.