As a kid on his grandfather’s ranch, Doug Anderson’s job was simple: Sit on the newborn calf and hold tight while his granddad slopped “black tar‑looking stuff” on its navel to guard against New World screwworm. Fifty years later, Anderson is back in the same fight — only now he’s supervising a USDA NWS strike team using aircraft, vehicles and release chambers and fluorescent‑dyed sterile flies to wipe out the parasite before it takes hold in Texas.
Anderson, a 22‑year tick rider and supervisor for USDA’s cattle fever tick eradication program, is helping blanket infested zones with 4 million sterile flies per week in an attempt to starve the parasite of its next generation.
While in South Texas last week, the Farm Journal team got a chance to watch Anderson and his team prepare and distribute a shipment of sterile NWS flies.
Why Sterile Flies?
Female NWS flies only mate once. When they mate with a sterile male, the eggs do not hatch. By releasing sterile NWS flies in and around affected areas, wild flies mate with them, preventing the production of viable offspring.
Anderson says the goal is to “saturate the area” so wild flies have no choice but to mate with sterile partners — and the life cycle stops.
USDA currently produces sterile flies for dispersal at the COPEG facility in Panama. USDA is also investing $21 million to support Mexico’s renovation of an existing fruit fly facility in Metapa — which will double NWS production capacity once complete, which is expected later this month. Moore Air Base near Edinburg, Texas, currently has a fly dispersal facility, where pupae from COPEG can arrive and be prepped for distribution. USDA is also building a production facility at Moore Air Base that is expected to be operational in the fall of 2027.
Guarding the Border, Protecting the Herd 🐄🪰@Screwworm_RR @USDA @USDA_APHIS @CBP @CBPSouthTexas pic.twitter.com/6G1nnqgG1G
— Director of Field Operations, Donald R. Kusser (@DFOLaredo) June 16, 2026
As of June 17, the number of sterile flies released in the U.S. in 2026 includes:
- Aerial dispersal: 135,623,026
- Ground dispersal: 12,079,200
- Vehicular dispersal: 5,238,496
“The locations and methods of dispersal change daily to ensure the most effective coverage,” explains Lyndsay Cole, USDA APHIS NWS directorate chief of strategic communications.
Cole reports there are about 40 aerial dispersal flights per week releasing approximately 100 million sterile flies in the dispersal area (shown on the map on this page and updated every Tuesday and Thursday). This week, about 40 million of the total sterile flies were released in the U.S.
Saturating the Skies: A Million Flies per Flight
The sterile flies being released by air originate from COPEG as pupae. They are then allowed to hatch at the facility in Edinburg and then are released over infested zones.
“Over each infested zone — every confirmed case of screwworm — the airplane releases a million sterile flies twice a week,” Anderson explains.
Pupae from COPEG arrive in the U.S., and members of USDA Strike Team pick up and transport them to Laredo where they are prepared for release.
A shipment of NWS sterile fly pupae arrives in Del Rio, Texas, from the COPEG facility in Panama, and then is driven to the USDA facility in Laredo.
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Members of the Strike Force team open each cooler and prepare for distribution the next morning. Each cooler contains 40 liters of pupae.
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Strike Force members measure out pupae for dyeing.
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Pupae are put into mixer for dyeing.
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Sterile fly pupae that will be released in the U.S. are dyed fluorescent green. Pupae that will be released in Mexico are dyed fluorescent orange.
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The purpose is straightforward and practical: using a black light sterile flies are easily identified.
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After pupae are dyed they are returned to the coolers and allowed to dry.
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After the pupae are dry they are loaded back up on the truck to haul to their home for the night.
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The flies are hauled to a cooled trailer. There they are placed on trays as pictured here. Each tray hold 5 liters of pupae.
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The flies are kept at 45 degrees overnight to keep them from emerging.
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From Coolers to Pupae Trays
As you can tell by the photo gallery above, the process starts long before the fly emerges in a surveillance zone. Sterile screwworm pupae arrive in bulk and are dyed before cooling overnight and eventually loaded into release chambers the next morning.
Once the pupae are dyed and dried, they are kept in a temperature-controlled trailer overnight at 45 degrees. Anderson explains the temperature management is not just about comfort — it directly affects when and where the flies emerge.
Anderson recalls an instance where pupae warmed too quickly in the field as they start making their own metabolic heat. That experience helps guide how coolers are handled now — kept cold enough to delay emergence until pupae are in place at the release sites.
“Tomorrow morning, we will load up the vehicles, everybody will take out their coolers, and we go to the different sites where we have the release chambers,” Anderson explains.
Release chambers are hung in carefully chosen trees and brush in surveillance zones.
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The first step is removing the pupae casings that remain after the fly has emerged.
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Trays of pupae casing before recharging with new pupae.
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The casings are removed from the trays and placed in bags.
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Trays are filled with pupae that will emerge within 24 to 48 hours.
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Within 24 to 48 hours the sterile fly emerges, dries and then flies off to mate with a wild NWS fly.
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Charging the Ground Release Chambers
The backbone of the ground operation is a network of release chambers hung in carefully chosen trees and brush around each infested zone.
“We charge each release chamber with 80,000 pupae, so there will be 80,000 flies, and within 24 to 48 hours it will be coming out of each one of those release chambers.”
Ground chambers are located in the surveillance zone surrounding the infected zone. Anderson notes currently 24 release chambers are placed around the infested zone, each receiving that 80,000‑pupae charge. Those chambers don’t just get hung anywhere.
“We’ve got to be very careful. It’s not just go hang something in a tree,” he says. “There has to be plenty of cover. There needs to be vegetation on the ground, not just bare dirt, because these flies are going to emerge. They’re going to start crawling on the grass, on the branches. They need shade while they’re drying out.”
The timing is precise. Once charged, pupae typically emerge within about 24 hours, and then the new adults need another 12 to 24 hours to dry and strengthen before they can fly.
When everything goes right, the day after charging the release site is active with newly emerged — but not yet airborne — flies.
Those flies, marked with fluorescent dye, will soon disperse across the landscape in search of females. Anderson estimates the adults may disperse one to two miles initially and travel three to five miles over their lifespan, depending on conditions.
Producer Role: Report Every Wound, Every Time
Reporting suspected infestations is critical. When a case is identified and confirmed, sterile fly distribution is quickly evaluated, and officials work to shift dispersal to an affected area.
“If you see a wound, let us know,” he stresses. “Call USDA, call Texas Animal Health Commission, call Texas Parks and Wildlife.”
Anderson compares the sterile fly release to fighting a wildfire.
“We’re going to immediately start releasing sterile flies over that area and around that area,” he explains. “It’s kind of like a fire, you’re dousing it with water, and then you douse around it.”
For producers, that means reporting wounds early and often can bring a wall of sterile flies to their area before screwworm spreads through calves, pets or wildlife.
