New World Screwworm (NWS) is a dangerous parasitic fly that can cause severe and even fatal damage to livestock, pets, wildlife, and occasionally people. The pest is especially concerning because—unlike many other maggots that only feed on dead tissue—the screwworm larvae actively burrow into healthy, living flesh.

What makes screwworm so dangerous?

• Female flies lay eggs on open wounds or body openings.
• One female can lay up to 400 eggs at once, and up to 2,800 eggs in her lifetime.
• The eggs hatch into larvae (maggots) that eat living tissue, tearing at it with sharp hooks.
• As more larvae hatch and feed, the wound enlarges and deepens.
• If untreated, the infestation can lead to severe infection, tissue destruction, and death.

This is not a small or cosmetic problem—the damage is real, rapid, and devastating.

Is it in North Carolina today?

No. New World Screwworm is NOT currently present in the United States. It was eliminated using sterile-fly technology in:

• 1966 — full U.S. eradication
• 2017 — small re-introduction in the Florida Keys successfully removed

Today, USDA works with Panama to maintain a sterile-fly barrier to keep screwworm from moving northward from South America.

Where screwworm still exists

Currently endemic in:

• Cuba
• Haiti
• Dominican Republic
• Several South American countries

The pest has slowly been spreading northward through Central America and Mexico—this is why continued awareness matters.

Recognition

Symptoms include:

• Persistent irritation or discomfort
• Head shaking or rubbing
• A foul “rotting” odor
• Presence of worms in or around a wound

Even a small cut—like an ear tag wound or castration site—can become a screwworm entry point.

Eradication

Screwworm females mate only once in their ~21-day life cycle. Scientists use this against them:

• Millions of sterile males are released.
• Females mate with sterile males.
• Eggs don’t hatch.
• The population collapses.

This biological control method is still used today as a defense barrier.You don’t need to panic—but you DO need awareness:

Maintain good wound care!

Clean and treat any cuts, dehorning sites, castration wounds, or injuries.

Watch livestock closely!

Check daily for unusual irritation or odor around wounds.

New World Screwworm is not here now, but it is a serious threat if it ever enters the U.S. again. Understanding the signs and reporting quickly can prevent an outbreak.

Visit USDA's Stop Screwworm Portal to learn more!