A fly that deposits its parasitic, flesh-eating offspring inside cows has been found in Texas for the first time in decades, The US Department of Agriculture (USDA) reported Wednesday (June 3).
Here’s what you need to know about New World screwworms (Cochleomyia hominivorax), a pest that was eradicated from the United States in the 1960s.
What is New World Screwworm?
New World screwworms are parasites that feed exclusively on the living flesh of warm-blooded animals, According to the American Society for Microbiology (ASM). Screwworms are the larvae, or maggots, of adults. C.hominivorax Flies.
Flies lay their eggs in open wounds or open places on the body of animals, such as eyes, ears, nose, mouth or genitals. Once the eggs hatch, the worms burrow into their host’s flesh using a screw-like motion, giving the species its name. The insects have sharp barbs in their mouths that can cause extensive damage, deepening the wound and increasing the chance of secondary infection. Infection can be painful, cause swelling and bleeding, and produce a foul odor.
after eating for about a weekThe insects enter their next stage of development and exit the animal, burrow into the soil to form a “pupate” and mature into a fly.
New World screwworms have distinct hooks (white arrows) in their mouths that they use to tear the flesh of their host.
(Image credit: Courtesy US Centers for Disease Control and Prevention)
Broadly speaking, worm infestations are known as myiasis, and myiasis caused by New World screwworms is a major problem for livestock agriculture. Places where the species of fly is found localor widespread, annual economic losses due to the fly could amount to billions of dollars each year. flies mostly infects large hoofed animalsLike cows, sheep and horses. Less commonly, they can infect domestic dogs and wild mammals, such as deer, rabbits, opossums, and birds.
Can screwworm infect humans?
Yes, New World screwworms can occasionally infect humans, although this is quite uncommon. Flies can potentially infect any warm-blooded animal, but livestock are most affected.
Get the world’s hottest discoveries delivered straight to your inbox.
People in endemic areas who work with animals, have weakened immune systems, sleep outside, or who have open wounds – no matter how small – are at highest risk of developing it. C.hominivorax Infections Like animals, infections in humans can be fatal, but they can be treated by physically removing the worms from the body.
Symptoms of infection include feeling or seeing insects moving around inside a skin lesion or wound, or in the ears, nose, eyes, or mouth; Developing painful sores or wounds on the skin that get worse within a few days; bleeding from wounds; And a foul odor at the site of infection.
This chart shows the life cycle of New World screwworms.
(Image credit: Courtesy US Centers for Disease Control and Prevention)
Screwworms are not spread from infected animals to people or from one person to another. Infection begins when the female fly lays eggs in a wound or body opening, such as the eye.
America reported this in 2025 New World’s first screwworm infection in a person In decades. The man, in Maryland, had returned to the US after traveling to El Salvador, where the fly is endemic. the person recovered With treatment.
Can infected livestock be treated?
Yes, livestock infected with New World screwworm can be treated with antiparasitic medications. Treatment also includes physically removing the maggots from the meat and disinfecting the wound sites. ASM notes that treatment must be timely, as infection can kill livestock in 10 days.
Here, you can see the screwworms’ sharp, curved mouth hooks (black arrow) and spiracles (white arrowheads), or openings in their exoskeleton.
(Image credit: Courtesy US Centers for Disease Control and Prevention)
Instead of killing the whole herd – similar to What has been done for commercial flocks infected with bird flu -According to the USDA, affected farms are being screened for additional cases and animals are not allowed to be taken off the premises during that time. Infected animals are treated and isolated until their wounds heal and they remain without any signs of infection for a few weeks. Euthanasia may sometimes be necessary for individual animals if infection is very widespread.
The USDA says animals that have recovered from screwworm myiasis can enter the food supply if they meet all regulatory requirements. Specifically, screwworms do not infect dead meat, only healthy, living meat. Thus screwworms pose a threat to food production but not to food security.
Is it a big deal that it’s been spotted in Texas?
Screwworm outbreaks can be incredibly costly if not stopped quickly – which is why the US has put so much effort into eradicating this pest. Experts predict that, if a large-scale outbreak hits the state today, Texas’ economy could collapse. Livestock industry disruption caused $1.8 billion loss. food prices will be expected to increaseIn exchange for.
After an extensive effort, which included releasing sterilized male flies into the wild and breaking the species’ reproductive cycle, the New World screwworm was declared eradicated from the continental US in 1966. Despite this local eradication, the US has still seen some large outbreaks of screwworm due to flies and infected animals entering the country from Mexico. The 1972 outbreak was the worst outbreak recorded after abolition, affecting several states and causing Thousands of cases in Texas alone.
A joint effort between the US and Mexico was established to prevent similar outbreaks in the future, and the parasite was largely eliminated. It was eradicated in Mexico in the 1980s.. But in recent years there have been signs of a comeback. Cases are moving north from Central American countries like Panama and Costa Rica. from 2023. In response, the US has implemented a strategy led by USDA run matters back down.
Adult screwworm flies lay eggs in the bodies of animals.
(Image credit: Image courtesy of the United States Department of Agriculture, Animal Plant Health Inspection Service.)
“All models show New World screwworm entering the country by 2025,” the USDA’s June 3 statement said, “but these efforts are likely to buy the country some time.”
So, find out C.hominivorax The incident in a 3-week-old calf in Zavala County, Texas was not surprising but required quick action. The case occurred in southwest Texas, about 50 miles (80 kilometers) from the U.S.-Mexico border. Worms were seen around the umbilical cord of the calf. The calf will recover with treatment, Agriculture Secretary Brooke Rollins told the associated press (AP).
“USDA urges residents to contact your veterinarian immediately if you notice any suspicious wounds, worms or infections in your animals or herd,” the agency said. said on x. “If you notice signs of worm infestation in live or recently deceased wild animals, especially in areas near the US/Mexico border, please call 866-4USDA-WS (866-487-3297) to report it to your local USDA Wildlife Service office.”
The agency is now pursuing the strategies and actions outlined in NWS Response Playbook To avert any potential danger in Texas. This includes setting up a quarantine zone around where the case was detected and limiting the movement of animals in that area.
According to the AP, Rollins said the USDA is so confident in its preparedness that it believes “there is no risk of widespread infection.” “There is no reason to believe that the pest will become established in our country as a result of this incursion,” he said.
This article is for informational purposes only and is not intended to provide medical advice.