As the New World screwworm continues its push northward in Texas, wildlife professionals, livestock producers, hunters and conservationists are understandably focused on where it might show up next. No one knows exactly how far this outbreak could spread, and predicting that would be irresponsible. But history gives us something valuable—a look at where this devastating parasite has gone before.
One of the most fascinating resources I’ve come across is a historical map published by Oklahoma State University Extension showing the migration of New World screwworm during the major 1951 outbreak. The map doesn’t depict today’s outbreak or attempt to forecast tomorrow’s. Instead, it illustrates where screwworms spread during that historic event, where they survived the winter of 1951-1952 and where they commonly overwintered during average years before eradication.
Looking at it today is impossible to ignore.
The light blue portion of the map covers a remarkable area of the southern United States, stretching from Southern California across Arizona, New Mexico and Texas before reaching into Oklahoma, Arkansas and parts of the Gulf Coast. In other words, history shows that under favorable conditions, screwworms were capable of expanding across a huge portion of the country. The darker shades represent areas where the flies actually survived the winter, allowing populations to persist into the following year without having to migrate north again.
That doesn’t mean those same areas will become infested in 2026. Weather patterns, surveillance efforts, livestock management and, most importantly, the sterile insect technique have dramatically changed the equation since the 1950s. Still, if we’re talking about a cone of possibility, this map deserves serious attention because it represents places that have historically supported screwworm populations.
As someone who has spent much of this year reporting on the screwworm situation, I immediately began thinking beyond livestock. Cattle understandably receive much of the attention because of the enormous economic consequences of an outbreak, but wildlife has just as much at stake. White-tailed deer, mule deer, desert bighorn sheep, elk, pronghorn and countless other mammals can all become hosts if they have an untreated wound.
It can impact any warm-blooded animal.
That is one reason wildlife agencies have become deeply involved in monitoring the current situation. A widespread screwworm outbreak wouldn’t simply affect agriculture. It could reshape wildlife management across large portions of the southern United States and northern Mexico.
Check out out interview about screwworm with legendary whitetail biologist Larry Weishuhn.
One of the encouraging aspects of this situation is that we are not fighting an unknown enemy. The United States successfully eradicated New World screwworm decades ago through one of the greatest insect control programs ever undertaken. Today’s response benefits from modern diagnostics, coordinated surveillance, sterile fly production, interstate cooperation and a wealth of scientific knowledge that simply didn’t exist during the 1951 outbreak.
Even so, history has value because it reminds us what this insect is capable of when conditions are favorable.
Too often, people view historical maps like this as either predictions or relics. They’re really neither. They’re reminders. They remind us why vigilance matters, why containment efforts deserve public support and why wildlife professionals, ranchers and government agencies are taking this outbreak so seriously.
When I look at this map, I don’t see a forecast.
I see a warning from history.
The areas shown here aren’t places that will necessarily be impacted in the months ahead. They are places that history tells us could be impacted if screwworm were ever allowed to gain the upper hand again.
Hopefully, we never allow that to happen.
Chester Moore
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