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How Sex and Scientific Research Saved Your Steak Dinner (and Bambi) From the Screwworm Fly—Again

screwworm fly

By releasing sterile male screwworm flies, scientists were able to eradicate the devastating pest after World War II—and they were able to control the fly once again after it re-emerged in 2016. The sterile male screwworm fly (Cochliomyia hominivorax) pictured above is marked with a numbered tag to study dispersal, behavior, and longevity. (Photo credit: Peggy Greb, USDA Agricultural Research Service,

By Susan J. Weller, Ph.D., and Robert K.D. Peterson, Ph.D.

If there is one thing that we have learned from scientific research, it’s this: We cannot know where the next breakthrough will come from, but maintaining adequate funding for our nation’s scientific researchers is money well-spent. As an example, consider the screwworm fly in the Florida Keys.

Susan Weller

Susan J. Weller, Ph.D.

For nearly 70 years, the U.S. federal government and international partners have been deploying a highly successful, if surprising, technique to deal with this devastating pest of cattle, pets, and other animals—releasing more screwworm flies. But the released flies are special; custom-reared in the lab to be sterile and so unable to mate or reproduce.

Though the name of the screwworm fly (Cochliomyia hominivorax) may sound silly, anyone who knows its potential damage isn’t laughing. Managing the ravages of this deadly pest used to cost ranchers hundreds of millions of dollars a year. These pests can deliver a gruesome and painful death to a full-grown cow in less than two weeks. The females lay their eggs in open wounds and, if left untreated, the maggots eat the living parts of the animal.

Bob Peterson

Robert K.D. Peterson, Ph.D.

In the 1930s, two enterprising young U.S. Department of Agriculture scientists, Edward Knipling and Raymond Bushland, weren’t satisfied just treating symptoms. To control the problem, they had to focus more on the screwworms. Their idea was to find a way to sterilize promiscuous male screwworm flies and then release them in the wild, overwhelming the fertile native flies, and crashing the population. The problem was one of scale – how to mass-castrate enough flies to have an effect?

Their breakthrough came after WWII when they read about unrelated research on the unusual effects of radiation. They applied this fundamental research to develop the “Sterile Insect Technique” or “SIT.” From 1957 to 2006, the USDA deployed SIT with the help of state governments and local ranchers, unleashing a wave of eradication across the American south and into Central America, effectively saving the cattle industry in the United States.

But October 2016 brought an unfortunate reminder of the importance of continued scientific monitoring in our modern era of globalized trade and travel: in the Florida Keys, the endangered Key deer had screwworm.

Thanks to continued research investments by the USDA to keep SIT current, the federal government and state of Florida were able to rapidly respond. In late March, after months of sterile fly releases and other treatments for the deer, the USDA announced that it had re-controlled the pest.

The lesson of the screwworm should be obvious—investment in scientific research pays dividends.

The effectiveness of SIT has improved since it was first developed and today this technique is used not just to treat screwworm, but to deal with the ravages of tsetse flies, fruit flies that threaten many food crops, and even the mosquitoes that transmit the Zika virus.

The President has proposed a more than 20 percent cut to the USDA’s budget, potentially endangering agricultural research and crucial monitoring programs. We cannot let short-term budget-cutting goals undermine successful long-term efforts that are economically essential to major U.S. industries like cattle. Fundamental research into something as seemingly esoteric as a fly’s sex life is a smart investment for the nation.

Further spread of the screwworm fly in the American South would be devastating to the endangered species like the Key deer, the U.S. cattle industry, American consumers, and their pets. But thanks to federal investment in research and the laudable work of the USDA and partners in Florida, we have beaten back this threat. Again. We don’t know where the next game-changing advance will come from, but funding our nation’s researchers to advance the frontiers of science—even when their investigations sound odd or obscure—has proven time and again that science returns tremendous benefits to society.

Susan J. Weller, Ph.D., is Director and Professor at the University of Nebraska State Museum in Lincoln, Nebraska, and 2017 President of the Entomological Society of America.

Robert K.D. Peterson, Ph.D., is Professor of Entomology at Montana State University in Bozeman, Montana, and 2017 Vice President-Elect of the Entomological Society of America.

Editor’s note: This article was developed in collaboration with the American Association for the Advancement of Science. Portions have been adapted from messaging shared with ESA and AAAS stakeholders for dissemination in other publications.


  1. This is the first politically written article I have read on this site. Please stop…I throughly enjoy the science, but this political stuff, if it continues, will induce me to unsubscribe. Thanks for all the great information on insects.

  2. The resurgence of Cochliomya is unfortunate. As l teach SMRM in class, l always say America has gone beyond the problem that we grapple with in the tropics. With the background information of Knipling, lm sure the Entomologists will deal adevastating blow to the problem, with improvement, as they are already doing with other insect species. No research, no development, therefore, funding is inevitable

  3. In my view this is an important statement on the value of research to the producer, the consumer, the nation. In the arena of funning, science and politics frequently cross paths. It is essential that the body politic be informed in order for them to make critical desions of taxpayer dollars. Good article, provide more of this type information.

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