Taming of the Screw, Act Three.

I’d never heard of the Darien Gap; what about you? It’s kind of a unique place on the planet that we and our Central American partners have been able to utilize in the fight against this predatory maggot, the New World Screwworm. It’s the last thing before Colombia, the narrowest part of the junction between North and South America, a spindly isthmus separating the Pacific and Atlantic Oceans. Its claim to fame is the harsh and unforgiving nature of its geography, composed of mountains and rain forest that form a brutal barrier between the two continents. It contains no road and is the only such place in all the thousands of miles that separate the polar ends of North and South America.

The Darien Gap is inhabited by about 8,000 indigenous people, who have made their peace with its punishing landscape. The rest of the planet, if they care about it at all, only have interest in getting from one end to the other. These folks are mainly refugees, desperate to escape their own punishing circumstances, and eccentric-seeming adventurer types. (One guy made it his mission to travel on foot from Tierra del Fuego all the way to Alaska, and another traversed this area, also on foot, dragging a 12-foot wooden cross.) Here sits the strategically-placed COPEG facility, fired up in 1985 and churning out a very special brand of screwworm fly, the kind that exclusively fires blanks. It runs 24 hours a day and produces some 20 million flies per week, which are sprayed out of airplanes over Panama and the surrounding areas. The fly-rearing folks have perfected the recipe for their world-famous maggot diet, and cardboard boxes are no longer used. The flies are kept chilled so that they wake up, warm and free, just after exiting the belly of the plane. COPEG has six outpost facilities which employ a team of veterinarians to examine cattle, treat wounds, and educate nearby ranchers. Researchers are working out how to exclusively hatch male flies, since sterile female flies do not contribute to the project’s efficiency. Field scientists trap and inspect adult insects to monitor the success of the program.

All that costs about 15 million US dollars per year and is estimated to save well over a billion. It was working like a well-oiled machine for forty long years… right up until it wasn’t. New detections of this pest abruptly skyrocketed in Panama during the summer of 2023, then raced north through all of Central America into Mexico during 2024 and 2025. How did NWS get the upper hand after all these years? It may be difficult to pinpoint a single cause, but experts believe that increased human and animal movement through the area acted together with a series of mild winters to tip the balance. The most recent documented case of screwworms was just a few weeks ago in Sabinas Hidalgo, which is a Mexican city less than 70 miles away from the Texas border. U.S. livestock producers are already sweating bullets over the screwworm’s rapid approach. In our next piece, you will (finally) learn what it all has to do with you.

Dr M.S. Regan