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
Follow Chester Moore and Higher Calling Wildlife® on the following social media platforms
To support the efforts of Higher Calling Wildlife® click here.
Subscribe to the Dark Outdoors podcast on all major podcasting platforms.
Higher Calling Wildlife on Facebook
Email Chester at chester@chestermoore.com.
I was born in 1950, lived southeast of san antonio in an area generally regarded as the post oak savannah. my dad ran cattle and i remember as a pre-teen checking for new born calves virtually daily so that their navels could be treated to prevent screw worn infestations because it was almost a certainty they would be infested. i didn’t think about it at the time but whitetails would be as severely target by the flies. in those days if you hunted whitetails you were lucky if you saw 4 or 5 deer in a season. then deer hunting was “deer” hunting not buck hunting if you know what i mean, compounding the deer population problem. by the time i reached my teen years the screw worm fly eradication program was in full swing and suddenly every time you sat deer hunting it was common to see a dozen to twenty deer during a sit. Hope the government is equally successful this time around!
Thanks for sharing your perspective! It’s an interesting story to follow.