Pest worms its way in
Expert says parasitic fly is unlikely to affect meat prices at grocery stores
New World screwworm larva
U.S. secretary of agriculture Brooke Rollins holds a briefing about the new World screwworm June 8 at the Knipling-Bushland U.S. Livestock Insects research Laboratory in Kerrville, Texas.
A cow is seen in a pasture June 6 near La Pryor, Texas, three days after the U.S. Department of Agriculture confirmed the New World screwworm was detected in a Texas calf.
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As of June 22, the Department of Agriculture recorded 16 confirmed cases of New World screwworm in the United States, mostly in Texas.
As the pest continues to make national headlines, many consumers wonder what it may mean for grocery store prices.
Oklahoma State University's Extension livestock marketing specialist, Derrell S. Peel, provided his expert opinion.
What is it?
The New World screwworm is a parasitic fly native to the northern hemisphere that invades warm-blooded animals to lay its eggs. Unique compared to other flies, the maggot feeds on the living flesh of its host.
"It will invade any warmblooded animal that it finds an opening into, like a wound or even a body opening," Peel said. "It can get in there, and these maggots then will set up housekeeping and start eating the animal while it's alive."
Infestation is not fatal if treated in a timely manner.
"If you treat them, the animals typically recover fine as long as you catch it early, before they do much damage to the animal," Peel said. "But it's a huge labor issue, cost issue, and time-consuming. You've got to check these animals very, very frequently. So there's a lot of cost involved for the producers."
How will it affect prices?
Peel does not predict this outbreak will affect meat prices consumers see in grocery stores.
"This thing is not going to affect cattle prices, and it's not going to affect beef production, because not that many animals are involved," he said. "It's not going to kill very many animals. It may kill a few if we don't find them in time. But in terms of the broader market, it's not going to be a market impact."
Many consumers remember the widespread effects from last year's avian influenza, or bird flu, outbreak that caused egg prices to skyrocket, reaching an average of nearly $6 per dozen in February 2025. That was the result of the eradication of millions of birds in the U.S., which led to issues in the supply chain, elevating prices.
"The screwworm is a fly, so it's a pest, which is an important distinction in terms of its impacts on cattle," Peel said. "It's not like an infectious disease or something. It's simply a pest."
An infectious disease like avian influenza can rapidly spread from bird to bird among a flock and has no viral treatment.
Screwworm, in contrast, "affects animals on a one-on-one basis and doesn't spread beyond what the pest itself spreads," Peel said. "One animal can have it, and an animal right next to it may never be impacted."
"The only mortality here is if you just fail to catch an animal in time, they will die a horrible death in about two weeks if left on their own," Peel said. "But it's not at all comparable to avian influenza because we're not talking about a disease that spreads across an entire population of animals."
Peel noted the outbreak affected the market when U.S. Agriculture Secretary Brooke Rollins closed southern border ports to the livestock trade in July 2025.
"The only impacts that we've had that are related to screwworm we've already seen, and that's the fact that the Mexican border has been closed for the last 18 or 20 months," Peel said. "That did have some impact because it reduced our tight supplies of feeder cattle even more, but we've already dealt with that."
What about safety?
Peel says screwworm presents no threat to the safe consumption of meat and is not a food safety issue.
"This particular fly or these maggots from the flies actually only impact living animals; they wouldn't even stay on a dead animal, and they certainly don't get into the meat," he added. Even animals with a prior screwworm infection, once treated and healed, are safe to enter the U.S. food supply.
How did it get here?
The New World Screwworm was discovered over 70 years ago and eradicated from the U.S. before it was reintroduced this year.
"These flies are also unique in that they only mate once in their life, and so they discovered a long time ago that if you release sterile male flies in the area where you have them, the females will breed with them," Peel said. "They only breed one time, and sterile males won't produce any eggs, and so they eventually breed themselves out of existence if you can saturate an area with these sterile flies."
He noted the screwworm fly population is typically less dense than the average house fly.
The U.S. government and Mexico were able to establish sterile fly facilities across North America to push the screwworm to the barrier of Panama.
"Basically, how it got around the barrier is through illegal movement," Peel said.
"So they were moving cattle through regions that we weren't dropping flies because we didn't know they were there."
Mexico reported more than 185,000 animals affected by the parasitic fly.
