The Screwworm Crisis: Why Florida Ranchers Still Fear This Forgotten Parasite

In the quiet pastures and barns of rural America, few pests have left as devastating a mark as the screwworm fly. Known scientifically as Cochliomyia hominivorax, the screwworm may look like an ordinary blowfly, but its larvae are anything but harmless. These flesh-eating parasites burrow into open wounds of warm-blooded animals—livestock, wildlife, and even humans—causing immense suffering, secondary infections, and, if left untreated, death. For Florida ranchers and American farmers alike, the screwworm represents more than just an agricultural threat—it’s a nightmare that once spanned decades and cost millions. The USDA has posted lots of historical data regarding this invasive parasite. Link.

A Look Back: The Mid-20th Century Epidemic

In the 1930s through the 1950s, screwworms wreaked havoc across the southern U.S., with Florida, Texas, and other Gulf states hit particularly hard. Cattle producers saw their herds decimated. The USDA estimates that screwworm infestations cost the livestock industry over $100 million annually in lost animals, treatments, and decreased productivity during the height of the epidemic.

This wasn’t just an inconvenience—it was a full-scale crisis. Animals were disfigured or killed by the larvae, requiring constant surveillance and treatment. My own grandfather—Pop—and his cousin Toby were hired out as cracker cowboys during the 1940s and ’50s to help ranches treat infected animals. And yes, this is a legitimate term. Florida Cracker refers to swamp cowboys who would ride and rope cattle, branding and treating them for ranchers before barbed wire was widespread across the state.

So, riding through the backwoods of Florida, they’d rope cattle, doctor wounds, and do what it took to keep the herds alive, specifically fighting screw worm infections. I remember my Pop saying how they would have to build a fire, heat a knife, and cut deep into some animals to save them and eradicate the fly. For them and so many others, the screwworm was no abstract threat—it was daily, dirty, hands-on work.

Eradication Success: A Modern Marvel

The solution came in the form of Sterile Insect Technique (SIT)—a pioneering method where millions of sterile male screwworm flies were released into the wild to disrupt the breeding cycle. The campaign, led by the USDA and state agricultural departments, took decades and a sustained effort to finally declare the U.S. screwworm-free by 1982.

Remember, screwworms first came to the US in the 1930's. This is fifty years of battle.

Since then, the U.S. has maintained a screwworm-free status through vigilance and cooperation with neighboring countries like Mexico and Panama, which serve as buffer zones using the same sterile insect approach.

In 2016, the screwworm reemerged in the Florida Keys, killing hundreds of Key deer and prompting swift emergency action. The outbreak was traced to an imported animal, reminding us just how fragile our biosecurity system can be. While it was ultimately contained, it showed that the threat isn’t behind us—it’s just at bay.

Why Import Caution Matters Today

In light of recent reports of screwworms detected in imported livestock and the growing volume of international animal trade, I personally support pausing certain imports until these pests can be effectively controlled at the source. This isn’t about fear—it’s about smart prevention and we fully support Brooke Rollins's decision, even though it may pose short term impacts, long term - this is the smart move.

Reintroducing screwworms into the U.S. could undo decades of eradication work and re-ignite a costly, cruel epidemic for ranchers and farmers who are already facing droughts, rising input costs, and regulatory pressures. It’s not just livestock at risk—screwworms threaten wildlife, pets, and public health, especially in warm states like Florida where conditions are ripe for infestation.

As stewards of the land and livestock, we must balance commerce with caution. It’s reasonable—and responsible—to enforce these temporary suspensions of animal imports when a known threat like the screwworm is involved. We've fought this battle before.

The scars are still there.

Just ask anyone whose family rode fence lines and treated cattle wounds in the heat of summer to save a herd like my Pop and Cousin Toby.

We shouldn't have to fight it again.