It’s the latest creepy crawler sparking alarm across America.
The US Department of Agriculture confirmed this week that the New World screwworm (NWS) was detected in a 3-week-old calf in Texas’ Zala County, with maggots clustered around its umbilical area.
The finding marks the first time the flesh-eating insect — which primarily targets livestock but can also infect humans — has been found in US cattle since it was eradicated nationwide in the 1960s.
A second case was confirmed Tuesday in Mexico’s Coahuila State, roughly 25 miles south of the Texas border, Reuters reported.
The latest detections come after years of the flesh-eating pest creeping north from Central and South America, fueling fears it could once again gain a foothold in the US.
So what do the latest infestations mean for Americans — and how serious is the threat? Here’s everything you need to know.
What are New World screwworms?
They’re parasitic flies attracted to wounds and body openings, including the eyes, ears, nose, mouth and genitals.
“Wounds as small as a tick bite may attract a female fly to feed and lay her eggs,” Dr. Casey Locklear, parasiticide lead and US Medical Strategic Lead at Elanco Animal Health, and a practicing veterinarian based in Texas, told The Post.
“A single female can lay 200 to 300 eggs at a time and may lay up to 1,000 eggs during her 10 to to 30-day lifespan,” she said.
The real danger begins when those eggs hatch.
“Unlike most fly species whose larvae feed on dead and decaying tissue, NWS larvae feed on living animals, causing severe tissue damage and even death if left untreated,” Locklear said.
The pest gets its name from the way the maggots burrow into living flesh in a spiral pattern — like a screw drilling into wood.
After feeding for about seven days, the larvae drop to the ground and burrow into the soil. They later emerge as adults that are roughly the size of a housefly, with orange eyes, metallic blue-green bodies and three dark stripes running down their backs.
What kind of threat do they pose?
Most infestations occur in warm-blooded animals, including livestock, pets and wildlife. Human cases are rare but can happen.
“While the immediate threat to public health is relatively low, the parasite’s capacity to devastate the cattle industry cannot be overstated,” said Dr. Tyler B. Evans, an infectious disease expert and founder and CEO of the Wellness Equity Alliance.
“Screwworm infestations in livestock lead to immense suffering, rapid herd losses and billions in potential economic damage if not swiftly contained,” he said.
That’s why experts say the concern extends far beyond ranches and farms.
“This is not just an agricultural issue — it’s a food security issue that affects every American,” Evans cautioned.
Still, there’s no reason to side-eye your groceries. New World screwworms do not infest meat, fruits, vegetables or other food products, according to the USDA.
What are the symptoms?
The most obvious sign is the presence of larvae inside a wound or sore, or in the ears, nose, eyes or mouth, according to the Centers for Disease Control and Prevention.
As the larvae feed, painful wounds develop and continue growing larger and deeper instead of healing as more eggs hatch. The sores often emit a foul odor and may bleed.
Secondary bacterial infections can also develop, triggering symptoms such as fever and chills.
Last year, the first US human case since the insects were eradicated was identified in a traveler who returned to Maryland from El Salvador. The patient recovered, and there was no evidence the infestation spread to other people or animals.
Can it be treated?
Yes.
In both humans and animals, treatment typically begins with manually removing visible larvae from the wound. Powders, antiseptic ointments and other treatments may then be applied to kill any remaining insects.
Patients should be monitored closely during recovery and treated for any secondary infections.
How can you stay safe?
“The best protection is straightforward,” Evans said. “Keep wounds clean, seek medical care quickly and remain alert if you’ve traveled through affected areas.”
For livestock producers and pet owners, education and vigilance are key, Locklear said.
“Contact your veterinarian immediately if you notice any open wounds, unusual swelling, discharge or signs of infestation,” she advised. “Keep wounds clean, covered and monitored while healing.”
The CDC recommends taking extra precautions when traveling to outbreak-affected countries, especially if you have a weakened immune system.
Suggestions include monitoring wounds and keeping them clean and covered, wearing long-sleeved shirts and pants that have been treated with an insecticide containing 0.5% permethrin and sleeping indoors.
Is there a major risk of spread in the US?
“This is a serious development, but it’s important to know that this is a manageable pest,” Locklear said.
The challenge is that screwworms can be difficult to eliminate once they’ve been established.
The US successfully wiped out the parasitic insects in the 1960s by releasing sterilized male flies. When female flies mated with them, they laid eggs that could not hatch. Because females reproduce only once, local populations eventually collapsed.
Now, federal and state officials are moving quickly to ensure history doesn’t repeat itself.
USDA and Texas authorities are establishing a 20-kilometer infected zone around the infestation site in Texas, where quarantines and surveillance measures will be enforced. Sterile flies are also being released into the area.
“USDA invested heavily in the tools needed to eliminate NWS ever since cases started increasing in Central America and Mexico,” Dudley Hoskins, under secretary for marketing and regulatory programs at the USDA, said in a statement. “The United States has defeated this pest before, and we will do it again.”
Authorities are also ramping up trapping efforts along the border and conducting targeted response operations near the outbreak.
“The US has one of the most effective surveillance and eradication programs in the world, built on decades of experience,” Evans said. “However, this only works if our government acts quickly and consistently.”
“The message is clear: vigilance and speed are our strongest defenses. Contain it early, and this remains an isolated incident,” he continued. “Fail to act decisively, and we risk turning a preventable outbreak into a national crisis.”
