What You Need to Know About New World Screwworms

It’s a worm! It’s a fly! It’s causing an infestation through Central America and into Texas!

It’s New World screwworm.

The flies that were eradicated from the U.S. in 1966 have, unfortunately, staged a comeback. They’ve been making their way north since 2023, and the U.S. Department of Agriculture (USDA) confirmed the first case in a U.S. animal at the beginning of June.

What Are New World Screwworms?

New World screwworms are actually parasitic flies. When female flies get ready to lay their eggs, they are attracted to the smell of wounds (even something as small as a tick bite) and other openings in the body (like eyes and nostrils), where they lay 200 to 300 eggs.

Once the eggs hatch, larvae burrow into the body and feed on living flesh before dropping down into the soil, emerging as adult flies a few days later.

Usually this happens to animals, but New World screwworms can also infest people and can be deadly if not treated.

How Did We Eradicate New World Screwworms Before?

The U.S. worked with Mexico and countries in Central America to release hundreds of thousands of sterile flies.

Scientists bred male flies in special facilities where they were exposed to radiation that sterilized them. Then, they released those flies. When they bred, the female flies laid eggs that could not hatch, stopping the fly lifecycle.

A large fly breeding facility in Panama created a biological barrier that kept flies from moving north from South America until recently.

Why Are New World Screwworms Back in the U.S.?

New World screwworms started to break through the biological barrier in Panama and show up in Mexico a few years ago, most likely because of disruptions to sterile fly production during COVID-19 and illegal cattle trade.

USDA invested in new sterile fly production facilities in Mexico and Texas, but unfortunately they did not become operational in time to prevent flies from reaching Texas livestock.

Am I in Danger New World Screwworms?

Probably not, but this is still a big deal. We’ve detected 12 cases of New World screwworm in U.S. animals as of yesterday, all in Texas and New Mexico.

The good news is that the government is taking action to stop the spread. The Texas sterile fly production facility is close to being operational, according to the USDA, which should help contain the flies.

USDA also announced over $100 million in funding for projects to strengthen detection, eradication, and rapid response. And the Food and Drug Administration issued an emergency authorization for a treatment for infected dogs and cats (though household pets are at low risk).

If you live somewhere that New World screwworm has been detected, protect yourself by:

• Keeping wounds clean and covered, even if they’re small
• Limiting exposed skin when outside with long-sleeved, loose clothing
• Using insect repellents and treating clothes with permethrin