U.S. Senator Roger Marshall of Kansas responded to screwworm infestation of livestock by blaming former President Joe Biden for allowing immigrants to carry the parasite into the United States “maybe on their flesh.”

Marshall, who previously represented the rural 1st District of Kansas containing approximately 4 million cattle, theorized on Newsmax and Bloomberg broadcasts Monday that Biden failed to do enough before leaving office 18 months ago to inhibit migration of a fly that lays flesh-eating larvae in animal hosts.

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The Republican senator praised President Donald Trump’s effort to combat spread of screwworm, which has been confirmed in livestock and a pet animal.

“This is another thing we can thank Joe Biden for — that when millions of people came out of Central America, they brought this screwworm with them. It was on their pets, maybe on their flesh as well,” Marshall said on Newsmax.

Marshall, who is running for reelection in 2026, received pushback from skeptics unconvinced the buck stopped with Biden. Remarks of the Kansas senator and physician also were criticized by the nonpartisan Kansas Coalition for Common Sense and the campaign of U.S. Senate candidate Adam Hamilton, who is seeking the Democratic nomination for Marshall’s seat in the Senate.

Lauren Fitzgerald, spokeswoman for the Kansas Coalition for Common Sense, said one-fourth of U.S. Department of Agriculture employees in the Animal and Plant Health Inspection Service, or APHIS, were forced out last year through budget cuts ordered by Elon Musk’s Department of Government Efficiency, or DOGE. APHIS serves as the nation’s primary defense against livestock disease outbreaks.

She said Marshall was among lawmakers who applauded DOGE cuts, which included programs dedicated to monitoring screwworm in Mexico and Central America.

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“Roger Marshall wants Kansans to believe he’s leading the fight against the screwworm, but he supported the very cuts that gutted USDA’s ability to protect Kansas ranchers,” Fitzgerald said. “Kansas farmers deserve better than politicians who vote one way in Washington and pretend they did the opposite when they’re back home.”

Tyson Brody, spokesman for the Hamilton campaign, said Marshall’s condemnation of the Biden administration was misplaced.

“Roger Marshall is doing what he does best: Running away and trying to blame anyone else for the consequences of his decision not to listen to Kansans,” Brody said.

In July 2025, Marshall took part in a news conference with USDA Secretary Brooke Rollins regarding the National Farm Security Action Plan. They were joined at the event by Department of Defense Secretary Pete Hegseth, then-Attorney General Pam Bondi and then-Department of Homeland Security Secretary Kristi Noem.

“I want to just commend the Department of Defense and all the agencies up here today for your joint efforts to combat disease — diseases like avian influenza, screwworm and foot and mouth — protecting our farmers and communities,” Marshall said.

On Monday, Marshall said the U.S. government was in the process of breeding in laboratories millions of sterile screwworm flies so they could be released into the wild to disrupt reproduction of the insect. The tactic could eventually help control outbreaks of screwworm, the senator said.

“I’m disappointed that the previous administration, the Biden administration, didn’t start making these screwworm male laboratories where we’re sterilizing these flies,” Marshall told Bloomberg.

Movement north of the fly led to a ban on shipments of live cattle from Mexico in May. That decision meant, on an annual basis, 1 million head of cattle wouldn’t enter the U.S. market.

USDA says screwworm flies lay eggs in wounds or openings of animals. The larvae hatch quickly and burrow into healthy tissue of cattle, horses, deer or other warm-blooded animals. Left untreated, the parasites spread infection rapidly before dropping off the host to reproduce.