ORLANDO, Fla. – One of the most devastating parasites in Florida’s history has once again been detected in the Sunshine State.
In a release last year, the Florida Department of Agriculture and Consumer Services announced that the New World Screwworm (NWS) had been moving northward through Mexico, posing a huge threat to the U.S.
But just last week, the USDA announced that a horse from Argentina had been presented for routine importation at a quarantine facility in Florida. There, officials found an open wound with NWS larvae.
[BELOW: New World Screwworm may be poised for a return to the U.S.]
However, Texas Ag Commissioner Sid Miller cautioned Florida residents not to panic.
“I want to set the record straight on the recent New World Screwworm detection in Florida,” he said. “This detection did not constitute evidence of a U.S. outbreak or domestic New World Screwworm infestation. It was thankfully caught during a routine inspection of an imported horse arriving from a country south of the Darién Gap.”
Per experts, the NWS are maggots that often enter animals through open wounds, feeding on an animal’s living flesh. As a result, infestations can be fatal if not treated.
“The New World Screwworm — a destructive parasite that targets warm-blooded animals — was eradicated from the U.S. more than four decades ago," state officials announced. “Its return would pose a serious threat to livestock, wildlife, and domestic animals, particularly in states like Florida with warm climates and abundant animal populations.”
Experts state that screwworm eggs are deposited in a “shingle-like manner” at the edges of superficial wounds, with larvae feeding by burrowing into the wound like a screw — hence the name.
While the NWS had been present in the southwestern U.S. since at least 1842, it was first documented as a major problem in 1933 after shipments of infested animals came in from the region.
At the time, the federal government and the state of Florida began developing tactics to deal with the threat, such as education programs, special insecticides, and radiation to sterilize the insects.
But in the meantime, producers lost out on tens of millions of dollars each year as the NWS ravaged livestock, data shows.
Eventually, the U.S. and Mexico worked together to push these infestations down to the southern borders of Mexico in 1986.
There was a brief reemergence in the Florida Keys affecting the endangered Key deer back in 2016, though the outbreak was ultimately eradicated.
However, Florida officials said that infestations have been spreading north from Panama since 2023, increasing the risk of this pest being reintroduced to the U.S.
As a result, health experts have been urging residents to keep an eye out for any signs of their return.
“This is about protecting American agriculture, plain and simple,” Florida Commissioner of Agriculture Wilton Simpson said. “We know how costly and dangerous this pest can be if it takes hold. We’re calling on Florida’s producers, veterinarians, and animal health professionals to remain aware and act quickly if they suspect something unusual.”
Last summer, federal officials rolled out a plan to preemptively combat the NWS by pushing eradication efforts in Mexico and setting up a facility in South Texas that can disperse sterile flies.
Later on, the USDA announced that it would be closing U.S. southern border ports to livestock trade as the infestation moved further northward. In 2025, the first case was reported domestically out of Maryland.
[BELOW: Florida woman gathers cold-stricken iguanas that fell from trees]
That said, Commissioner Miller explained that no outbreaks of NWS in the wild have yet been discovered in the U.S. As such, the risk to public health at the time of writing is still very low.
Signs of screwworm infestation in animals include the following symptoms:
- Wounds in living animals infested with maggots
- Blood-tinged discharge from the infested wounds
- Foul odor
- Discomfort
- Depressed/no eating
- Decreased milk production
- Seclusion from rest of herd or flock
If you come across a suspected case of screwworms or have questions about potential infestations, you can call the FDACS at (850) 410-0900 or click here.