The return of the new world screwworm: what you need to know
Robbie Jones
If you’ve spent any time scrolling through social media lately, you may have come across some alarming videos about an insect called the New World Screwworm (NWS). While some of these clips may sound dramatic, the threat is very real and growing. In 2023, NWS cases in Panama suddenly jumped from around 25 a year to over 6,500. This was a major red flag for scientists and agricultural officials.
The New World Screwworm is a dangerous parasitic fly. Its larvae, or maggots, feed on the living flesh of warm-blooded animals like cows, deer, pets, and even humans. The adult flies are about the size of houseflies. They have shiny blue bodies and orange eyes. Females lay their eggs in open wounds, and once the larvae hatch, they burrow deep into the tissue. If not treated, the infection can become deadly.
Back in the 1950s and 19660s, the U.S. Department of Agriculture (USDA) and state agriculture agency partners worked hard to get rid of this pest. By releasing millions of sterile male flies, they broke the fly’s life cycle and wiped it out from the United States. They even set up a “biological barrier” in southern Panama to keep the screwworm from spreading north again.
But now, the insect is moving north. After reappearing in Panama, it has slowly crept into Costa Rica, Nicaragua, Honduras, El Salvador, Belize, Guatemala, and southern Mexico. While it hasn’t reached the U.S. yet, experts warn that it could cross the border before new control systems are ready.
Some people online say it has been so long since we dealt with screwworm that there’s no way to stop it quickly. That’s not true. In 2016, the Florida Keys had a serious outbreak of NWS. It started when wildlife officers found Key deer with badly infected wounds filled with larvae. Testing confirmed that it was a screw worm. Over 130 deer died.
Federal, state, and local agencies jumped into action. The USDA, Florida Department of Agriculture and Consumer Services (FDACS), and the U.S. Fish and Wildlife Service worked together. They released about 154 million sterile flies to stop the screwworm from spreading. By March 2017, the outbreak was declared over.
What we learned from that experience is now being used to stop the current outbreak from spreading. On June 18, USDA Secretary Brooke Rollins announced a new action plan. The goal is to stop the screwworm from reaching the U.S. and push it back to the southern Panama barrier.
Here’s what the plan includes:
- Import Controls: USDA is limiting animal imports at the southern border to stop screwworm from sneaking into the country.
- New Facilities: Two new fly-rearing labs are being built to produce over 300 million sterile males each week.
- Surveillance and Trapping: States are working with USDA to monitor the situation closely.
- International Cooperation: USDA is teaming up with Mexico and Central American countries to stop the spread.
- Funding: Over $109 million is being spent to fight the outbreak.
In Florida, FDACS Commissioner Wilton Simpson has issued a statewide alert. Veterinarians, ranchers, livestock owners, and wildlife workers are being asked to keep a close eye on animals. If you see maggots or signs of infection, like strange wounds, swelling, or animals acting sick, call a vet, FDACS, or your local Extension office right away.
While some videos online may exaggerate the problem, the threat is real. If screwworm spreads into Texas or other parts of the southern U.S., the cost to the livestock industry could be as high as $1.8 billion. That’s on top of threats to wildlife, pets, food safety, and public health.
The 2016 outbreak in Florida cost more than $4 million to control. But it also proved that we know how to fight this pest and win.
The New World Screwworm was once considered defeated, thanks to one of the greatest scientific pest control efforts in history. Now, it’s trying to come back. With new funding, better facilities, and strong teamwork between federal and state agencies, we have the tools to stop it again.
Everyone has a role to play. Be alert, report what you see, and help spread good information and not fear. To learn more about or report a suspected case, call the Gadsden County Extension Office at 850-875-7255.
Robbie Jones is the Agriculture and Natural Resources Agent/County Extension Director for UF/IFAS Extension Gadsden County.
