Mandatory Screwworm Reporting

Many ranchers may not realize that when maggots or fly larvae are found on any live animal, it is a mandatory reporting instance as explained below.

NOTE: this article was originally published to LivestockWeekly.com on May 21, 2025. It was written by Colleen Schreiber.

Dr. Phillip Kaufman, head of the Entomology Department at Texas A&M University, has been designated the go-to person on the screwworm issue insofar as getting the facts out to the media.

His job is to help educate and ensure people understand the seriousness of the issue and the steps needed to prevent, or at least better manage, an infestation should it reach the U.S. again. A big part of that is surveillance, and simple things like regularly inspecting livestock.

“The sterile insect technique is just one part of an eradication program,” Kaufman stresses. “It's an absolutely critical part, but it is one part. There's a lot of surveillance and checking animals, physically removing the screwworm when they’re found, treating them, and rechecking them that also must be done.”
Kaufman was at the University of Florida when the outbreak occurred in the National Key Deer Refuge in Big Pine Key, Florida.

“There were lessons learned from that outbreak,” says Kaufman.

One big lesson learned was that people did not realize that when maggots or fly larvae are found on any live animal, it is a mandatory reporting instance. In the case of the Florida outbreak, someone did not do that. Thus, two months or so passed before it was detected in the Key deer when they began shedding velvet and the flies began laying eggs on those wounds. It took off from there.

“Had it been reported early, it probably could have been suppressed,” says Kaufman.

Now that the screwworm is real threat again, Texas A&M is working with other state partners to launch some trainings around the state. The issue is making sure the best, most up-to-date information is distributed.

Hereto, Kaufman understands the importance of this. He was directly involved in this part of the Florida effort. Because the screwworm had been eradicated back in the 1960s, the educational information available was outdated. He and a team of others put together new resource material which included what to do if maggots were found, point of contact for reporting, along with new imagery.

“There's all kinds of requests for this kind of material now, and we’re trying to make sure that we get the best information out there, that we get the correct experts to talk about their particular component,” Kaufman says.

The plan is to finish getting the educational pieces put together, then training of the trainers completed so that Texas AgriLife Extension can begin holding educational meetings around the state in the next few weeks.

“The response plan is in place; that comes through the Texas Animal Health Commission,” Kaufman notes. “That’s their responsibility. Extension and others are here to advise and assist in the educational aspect.”

The Texas Animal Health Commission and USDA-APHIS, have up to date information on the life cycle, clinical signs, transmission, diagnosis, reporting, prevention, treatment and eradication available on their respective websites. For example, the proper reporting protocol is that a suspect case must be reported within 24 hours by contacting a local veterinarian or one of the regional Texas Animal Health Commission offices.

He points out that there are lots of other blow flies that love to get on dead animals. The unique thing about the screwworm is it only lays its eggs on live animals.

“Not every maggot on a live animal is guaranteed to be a screwworm,” says Kaufman. “It takes an expert to confirm that it’s a screwworm. If it’s a dead animal, it’s not a screwworm unless the screwworm killed that animal.”

Also, if a case is confirmed, the animal will have to be treated per veterinarian recommendations, monitored and retreated until the wound is completely healed. Additionally, surveillance, trapping of wild flies, is another critical piece.
Kaufman also points out that because screwworm has been eradicated from the U.S. for several decades now animal health companies have not been registering pesticides for screwworms.

“That doesn't mean we don't have products that would kill the screwworm if found, but they're not registered, and so it's an illegal application if used off label,” Kaufman stresses.

Emergency exemptions would be required from the FDA if it’s a systemic drug that goes into the animal’s system or the EPA for a topical pesticide, for example, before those drugs could be used.

"There is a lot of talk that ivermectin can be used to control screwworm, but it does not carry screwworm on its label at this point,” he reiterated. “It doesn’t mean it can’t be approved but right now it is not.”

There are a host of questions that must be addressed before an emergency application could potentially be considered. Such things as treatment, timeline, including retreatment, dosage, and withdrawal periods for pesticide residue before it could enter the food chain for human consumption, must all be figured out through the scientific process.

A bigger issue than even the livestock is the wildlife population, and not just white-tailed deer, but a host of exotic ungulates and feral pigs that are also hosts for the screwworm that can’t be regularly inspected. That’s not to say there aren’t some tools that could potentially work for wildlife. One that is getting lots of attention on social media is ivermectin-treated corn that’s being used in the fever tick eradication program for the treatment of white-tailed deer which are a host for the fever tick. However, that product is not commercially available. It may only be used on a restricted basis, and the use of it is controlled and monitored through the appropriate federal agencies. For example, the ivermectin-treated corn may not be used after July so that the active ingredient can be out of the deer’s system prior to the start of hunting season.

Kaufman reiterates that rules are in place for a reason.

“There is simply no way to treat all the wildlife in South Texas with a pesticide or a parasiticide. It’s just not practical. It may be a tool in time, but in the end the only way we are going to regain control is by relying on the sterile insect technique and that’s going to require time and patience and partnerships with many countries.”

Work is underway to figure out the sterile fly production piece, namely the logistics for a new plant, the location, the timeline, the money and on and on. There are other technologies in the works as well, potentially a genetically modified fly, for example, but that work is still likely a couple of years out and time is of the essence.

Some are saying that the fly could be here within a couple of months; others say longer. Kaufman points out that the movement will really be driven by how animal movements are managed in Mexico, either legal or illegal.

“That’s how the fly is being moved, by infested animals being moved large distances. The fly itself does not fly 200 miles. It’s on an animal that is being driven somewhere.”

Thankfully it has not yet been detected in the U.S., but popular press has taken an interest. Kaufman has already done interviews with the Houston Fox TV station, with Newsweek, and he’s taken calls from news organizations as far away as Wyoming.

“There’s a lot of interest and rightly so. It’s important. An educated populous is important because it means smart decisions are more likely to be made.”

He also reminds educating the populous is important because it’s not only livestock and wildlife, but also domestic pets, and on rare occasions, even humans that may be impacted by a screwworm infestation.

“It’s when it’s not reported and goes untreated that the problems occur,” Kaufman reiterates. “Also, this is an animal health issue, not a food safety issue.

Unfortunately, I’ve already seen postings on social media where people are being told to cook their meat thoroughly to avoid contamination from the screwworm. That’s the type of thing that we’re trying to educate people about.”