The New World screwworm is a flesh-eating parasitic fly that has crept back into the U.S. after being eradicated for decades.
Adult screwworms lay eggs in open wounds and as maggots, they feed off healthy tissue. These infestations are painful and can affect livestock, pets, wildlife and in rare cases, people.
So far, the pest is lingering in Texas and there have been cases in southern New Mexico. Nothing has been reported in Oklahoma, one of the top states for beef cattle.
Historically, the fly was not present year-round in Oklahoma. It inched up north of the Red River during warmer weather, and would get pushed back south as temperatures cooled.
As people in the agriculture industry have closely watched the parasite for well over a year, there is a large response to preventing the insects' spread. Releasing sterile flies, which were used to eradicate the pest from the U.S. in the 1960s, has been key.
Jonathan Cammack, Oklahoma State University state extension specialist for livestock, entomology and parasitology, said releasing the sterile flies appears to be working.
"Because I think otherwise we'd see a lot more cases than we have over the past five weeks or so at this point," Commack said. "So that's good to see that that's actually working. Or at least, as a potential kind of explanatory factor as to why that spread isn't happening much faster within the state of Texas."
As of Monday, there have been about 35 cases reported to the U.S. Department of Agriculture.
There are specific environmental characteristics the insect needs to thrive, Cammack said. For adult flies and their offspring, he said they have a wide temperature window ranging from 59 degrees to about 111 degrees.
Cammack said the adults like an average temperature of about 78 to 80 degrees, which has been close to the daily average in Oklahoma recently. He said other pests seen in the summer are typically here year-round but screwworms can't survive cold weather.
"It's not quite the same, just from a purely biological standpoint, because they are pretty restricted by temperature and in that they can't overwinter some of those other life stages," Cammack said.
Although weather has a role in where the fly spreads, wildlife also plays a part. He said there is concern because wildlife populations are different from what they were 50-75 years ago when people last dealt with screwworms in the U.S.
For instance, there are larger white tail deer populations.
"Data suggests that back in the [19]60s that like 90% of the annual whitetail deer fawn crop was killed due to screwworm infestations just because of how abundant screwworms were," Cammack said.
At the same time, there are a lot of non-native wildlife such as feral hogs in nearly every Oklahoma county If a screwworm infestation goes unnoticed, it has the ability to spread quickly because of how fast animals move.
To control the fly, Cammack said people should watch the animals around them.
People outdoors should look at wildlife. Producers must frequently check livestock for wounds and get them treated because the worms need it to start an infestation. If big wounds or maggot-infest gashes are seen, Cammack said it needs to be reported.
"I think it's going to come down to this is going to take kind of a collaborative effort from essentially everybody to get under control," Cammack said. "And that really is going to come down to monitoring."
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