As USDA halts animal imports, UF experts explain the risk of the New World screwworm
4 March 2026
3 minute read
By: The Florida Department of Agriculture and Consumer Services (FDACS) is urging veterinarians, livestock producers, and animal health professionals to be vigilant and recognize the signs and symptoms of the New World screwworm, as the threat of its spread increases in the United States.
Screwworms could pose a threat to livestock, wildlife, and domestic animals, especially those linked to the U.S. food system, such as beef and dairy cattle. The threat is particularly serious in states with warm climates and abundant animal populations like Florida.
To help you better understand this insect, University of Florida experts explain what the New World screwworm is, why it represents a problem that the United States has successfully controlled in the past, and how to identify signs of screwworm infections in your animals.
What is the New World screwworm?
The New World screwworm is a type of fly, scientifically known as Cochliomyia hominivorax . The main concern lies with its larvae, as they feed on the living flesh of warm-blooded animals.
Grubs are the immature stage of the fly: the tiny, worm-like organisms that emerge from eggs. Unlike most grubs, which feed on dead tissue and contribute to the decomposition process, the New World screwworm feeds on living, healthy tissue. They use existing wounds as an entry point to burrow into the body of the living animal, causing severe damage and even death, explained Andrew Short, chair of the UF/IFAS Department of Entomology and Nematology.
Screwworms can infest livestock, pets, wildlife, sometimes birds, and even, rarely, humans.
All warm-blooded animals are at risk of infection, especially if they have exposed wounds or have recently undergone surgery.
When was the last time the United States had a screwworm outbreak?
The New World screwworm was present in the United States before the Civil War and was eradicated in 1966, Short said.
However, in 2016, an outbreak was detected in a population of Key West deer in the Florida Keys. The infection continued until early 2017, when it was eliminated from the environment through a biological control program using sterile flies.
Is a screwworm infection treatable?
Yes, New World screwworm infections are treatable. In humans and domestic animals, treatment generally requires manual or surgical removal of the larvae by medical or veterinary personnel. In wildlife, control efforts focus on eliminating screwworm flies from the environment.
How do you eliminate New World screwworms in a specific area?
The eradication of the New World screwworm is accomplished by releasing sterilized flies into the environment. These flies, unable to produce offspring, mate with wild screwworm flies. As a result, the population declines until it disappears completely.
What are the symptoms of a New World screwworm infection in animals?
Symptoms in animals infected with screwworm include irritable behavior, especially in relation to a wound, head shaking, biting at an open wound, foul odor from decaying tissue, presence of larvae (maggots) in the wound, a red bump caused by the infestation, signs of depression such as poor appetite, decreased milk production, and isolation from the rest of the herd.
The first symptoms can be difficult to detect, but the most obvious sign is a change in the wound's appearance: it becomes larger and deeper. It may also have a foul odor and bloody discharge, according to the FDACS.
Animal and livestock owners who suspect a screwworm infection should isolate the affected animal and immediately contact their veterinarian, said Dr. Fiona Maunsell, associate professor in the UF College of Veterinary Medicine. They should also report their suspicions to the State Veterinarian's Office.
Maunsell notes that owners should never treat a maggot-infested wound without first contacting their veterinarian or the State Veterinarian's Office, as this could delay timely detection and control of the outbreak.
Although any animal can become infected, animals that spend most of their time outdoors, especially those that give birth outdoors, are at greater risk due to the possibility of open wounds. To prevent infestations, it's important to keep wounds dry and covered, as well as report any signs of illness to your veterinarian.
How can I report a New World screwworm infection?
Early detection and reporting are essential, said Dr. Michael Short, Florida State Veterinarian, in an FDACS news release.
"The sooner we detect a potential case, the greater the chances of containing it. We ask everyone who works with animals, whether in private practice or in the field, to carefully review any unusual wounds or those that don't heal as expected," he stated.
If you suspect a case of New World screwworm infection in livestock or pets, contact your local or state veterinarian.
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