Science
California issues advisory on a parasitic fly whose maggots can infest living humans
A parasitic fly whose maggots can infest living livestock, birds, pets and humans could threaten California soon.
The New World Screwworm has rapidly spread northward from Panama since 2023 and farther into Central America. As of early September, the parasitic fly was present in seven states in southern Mexico, where 720 humans have been infested and six of them have died. More than 111,000 animals also have been infested, health officials said.
In early August, a person traveling from El Salvador to Maryland was discovered to have been infested, federal officials said. But the parasitic fly has not been found in the wild within a 20-mile radius of the infested person, which includes Maryland, Virginia and the District of Columbia.
After the Maryland incident, the California Department of Public Health decided to issue a health advisory this month warning that the New World Screwworm could arrive in California from an infested traveler or animal, or from the natural travel of the flies.
Graphic images of New World Screwworm infestations show open wounds in cows, deer, pigs, chickens, horses and goats, infesting a wide swath of the body from the neck, head and mouth to the belly and legs.
The Latin species name of the fly — hominivorax — loosely translates to “maneater.”
“People have to be aware of it,” said Dr. Peter Chin-Hong, a UC San Francisco infectious diseases specialist. “As the New World Screwworm flies northward, they may start to see people at the borders — through the cattle industry — get them, too.”
Other people at higher risk include those living in rural areas where there’s an outbreak, anyone with open sores or wounds, those who are immunocompromised, the very young and very old, and people who are malnourished, the U.S. Centers for Disease Control and Prevention says.
There could be grave economic consequences should the New World Screwworm get out of hand among U.S. livestock, leading to animal deaths, decreased livestock production, and decreased availability of manure and draught animals, according to the U.S. Department of Agriculture.
“It is not only a threat to our ranching community — but it is a threat to our food supply and our national security,” the USDA said.
Already, in May, the USDA suspended imports of live cattle, horse and bison from the Mexican border because of the parasitic fly’s spread through southern Mexico.
The New World Screwworm isn’t new to the U.S.
But it was considered eradicated in the United States in 1966, and by 1996, the economic benefit of that eradication was estimated at nearly $800 million, “with an estimated $2.8 billion benefit to the wider economy,” the USDA said.
Texas suffered an outbreak in 1976. A repeat could cost the state’s livestock producers $732 million a year and the state economy $1.8 billion, the USDA said.
Historically, the New World Screwworm was a problem in the U.S. Southwest and expanded to the Southeast in the 1930s after a shipment of infested animals, the USDA said. Scientists in the 1950s discovered a technique that uses radiation to sterilize male parasitic flies.
Female flies that mate with the sterile male flies produce sterile eggs, “so they can’t propagate anymore,” Chin-Hong said. It was this technique that allowed the U.S., Mexico and Central America to eradicate the New World Screwworm by the 1960s.
But the parasitic fly has remained endemic in South America, Cuba, Haiti and the Dominican Republic.
In late August, the USDA said it would invest in new technology to try to accelerate the pace of sterile fly production. The agency also said it would build a sterile-fly production facility at Edinburg, Texas, which is close to the Mexico border, and would be able to produce up to 300 million sterile flies per week.
“This will be the only United States-based sterile fly facility and will work in tandem with facilities in Panama and Mexico to help eradicate the pest and protect American agriculture,” the USDA said.
The USDA is already releasing sterile flies in southern Mexico and Central America.
The risk to humans from the fly, particularly in the U.S., is relatively low. “We have decent nutrition; people have access to medical care,” Chin-Hong said.
But infestations can happen. Open wounds are a danger, and mucus membranes can also be infested, such as inside the nose, according to the CDC.
An infestation occurs when fly maggots infest the living flesh of warm-blooded animals, the CDC says. The flies “land on the eyes or the nose or the mouth,” Chin-Hong said, or, according to the CDC, in an opening such as the genitals or a wound as small as an insect bite. A single female fly can lay 200 to 300 eggs at a time.
When they hatch, the maggots — which are called screwworms — “have these little sharp teeth or hooks in their mouths, and they chomp away at the flesh and burrow,” Chin-Hong said. After feeding for about seven days, a maggot will fall to the ground, dig into the soil and then awaken as an adult fly.
Deaths among humans are uncommon but can happen, Chin-Hong said. Infestation should be treated as soon as possible. Symptoms can include painful skin sores or wounds that may not heal, the feeling of the larvae moving, or a foul-smelling odor, the CDC says.
Patients are treated by removal of the maggots, which need to be killed by putting them into a sealed container of concentrated ethyl or isopropyl alcohol then disposed of as biohazardous waste.
The parasitic fly has been found recently in seven Mexican states: Campeche, Chiapas, Oaxaca, Quintana Roo, Tabasco, Veracruz, and Yucatán. Officials urge travelers to keep open wounds clean and covered, avoid insect bites, and wear hats, loose-fitting long-sleeved shirts and pants, socks, and insect repellents registered by the Environmental Protection Agency as effective.
Science
What’s in a Name? For These Snails, Legal Protection
The sun had barely risen over the Pacific Ocean when a small motorboat carrying a team of Indigenous artisans and Mexican biologists dropped anchor in a rocky cove near Bahías de Huatulco.
Mauro Habacuc Avendaño Luis, one of the craftsmen, was the first to wade to shore. With an agility belying his age, he struck out over the boulders exposed by low tide. Crouching on a slippery ledge pounded by surf, he reached inside a crevice between two rocks. There, lodged among the urchins, was a snail with a knobby gray shell the size of a walnut. The sight might not dazzle tourists who travel here to see humpback whales, but for Mr. Avendaño, 85, these drab little mollusks represent a way of life.
Marine snails in the genus Plicopurpura are sacred to the Mixtec people of Pinotepa de Don Luis, a small town in southwestern Oaxaca. Men like Mr. Avendaño have been sustainably “milking” them for radiant purple dye for at least 1,500 years. The color suffuses Mixtec textiles and spiritual beliefs. Called tixinda, it symbolizes fertility and death, as well as mythic ties between lunar cycles, women and the sea.
The future of these traditions — and the fate of the snails — are uncertain. The mollusks are subject to intense poaching pressure despite federal protections intended to protect them. Fishermen break them (and the other mollusks they eat) open and sell the meat to local restaurants. Tourists who comb the beaches pluck snails off the rocks and toss them aside.
A severe earthquake in 2020 thrust formerly submerged parts of their habitat above sea level, fatally tossing other mollusks in the snail’s food web to the air, and making once inaccessible places more available to poachers.
Decades ago, dense clusters of snails the size of doorknobs were easy to find, according to Mr. Avendaño. “Full of snails,” he said, sweeping a calloused, violet-stained hand across the coves. Now, most of the snails he finds are small, just over an inch, and yield only a few milliliters of dye.
Science
Video: This Parrot Has No Beak, But Is at the Top of the Pecking Order
new video loaded: This Parrot Has No Beak, But Is at the Top of the Pecking Order
By Meg Felling and Carl Zimmer
April 20, 2026
Science
Contributor: Focus on the real causes of the shortage in hormone treatments
For months now, menopausal women across the U.S. have been unable to fill prescriptions for the estradiol patch, a long-established and safe hormone treatment. The news media has whipped up a frenzy over this scarcity, warning of a long-lasting nationwide shortage. The problem is real — but the explanations in the media coverage miss the mark. Real solutions depend on an accurate understanding of the causes.
Reporters, pharmaceutical companies and even some doctors have blamed women for causing the shortage, saying they were inspired by a “menopause moment” that has driven unprecedented demand. Such framing does a dangerous disservice to essential health advocacy.
In this narrative, there has been unprecedented demand, and it is explained in part by the Food and Drug Administration’s recent removal of the “black-box warning” from estradiol patches’ packaging. That inaccurate (and, quite frankly, terrifying) label had been required since a 2002 announcement overstated the link between certain menopause hormone treatments and breast cancer. Right-sizing and rewording the warning was long overdue. But the trouble with this narrative is that even after the black-box warning was removed, there has not been unprecedented demand.
Around 40% of menopausal women were prescribed hormone treatments in some form before the 2002 announcement. Use plummeted in its aftermath, dipping to less than 5% in 2020 and just 1.8% in 2024. According to the most recent data, the number has now settled back at the 5% mark. Unprecedented? Hardly. Modest at best.
Nor is estradiol a new or complex drug; the patch formulation has existed for decades, and generic versions are widely manufactured. There is no exotic ingredient, no rare supply chain dependency, no fluke that explains why women are suddenly being told their pharmacy is out of stock month after month.
The story is far more an indictment of the broken insurance industry: market concentration, perverse incentives and the consequences of allowing insurance companies to own the pharmacy benefit managers that effectively control drug access for the majority of users. Three companies — CVS Caremark, Express Scripts and OptumRx — manage 79% of all prescription drug claims in the United States. Those companies are wholly owned subsidiaries of three insurance behemoths: CVS Health, Cigna and UnitedHealth Group, respectively. This means that the same corporation that sells you your insurance plan also decides which drugs get covered, at what price, and whether your pharmacy can stock them. This is called vertical integration. In another era, we might have called it a cartel. The resulting problems are not unique to hormone treatments; they have affected widely used medications including blood thinners, inhalers and antibiotics. When a low-cost generic such as estradiol — a medication with no blockbuster profit margins and no patent protection — runs into friction in this system, the friction is not random. It is structural. Every decision in that chain is filtered through the same corporate profit motive. And when the drug in question is an off-patent estradiol patch that has negligible profit margins because of generic competition but requires logistical investment to keep consistently in stock? The math on “how much does this company care about ensuring access” is not complicated.
Unfortunately, there is little financial incentive to ensure smooth, consistent access. There is, however, significant financial incentive to steer patients toward branded alternatives, or simply to let supply tighten — because the companies aren’t losing much profit if sales of that product dwindle. This is not a conspiracy theory: The Federal Trade Commission noted this dynamic in a report that documented how pharmacy benefit managers’ practices inflate costs, reduce competition and harm patient access, particularly for independent pharmacies and for generic drugs.
Any claim that the estradiol patch shortage is meaningfully caused by more women now demanding hormone treatments is a distraction. It is also misogyny, pure and simple, to imply that the solution to the shortage is for women’s health advocates to dial it down and for women to temper their expectations. The scarcity of estradiol patches is the outcome of a broken system refusing to provide adequate supply.
Meanwhile, there are a few strategies to cope.
- Ask your prescriber about alternatives. Estradiol is available in multiple formulations, including gel, spray, cream, oral tablet, vaginal ring and weekly transdermal patch, which is a different product from the twice-weekly patch and may be more consistently available depending on manufacturer and region.
- Consider an online pharmacy. Many are doing a good job locating and filling these prescriptions from outside the pharmacy benefit manager system.
- Call ahead. Patch shortages are inconsistent across regions and distributors. A call to pharmacies in your area, or a broader geographic radius if you’re able, can locate stock that your regular pharmacy doesn’t have.
- Consider a compounding pharmacy. These sources can sometimes meet needs when commercially manufactured products are inaccessible. The hormones used are the same FDA-regulated bulk ingredients.
Beyond those Band-Aid solutions, more Americans need to fight for systemic change. The FTC report exists because Congress asked for it and committed to legislation that will address at least some of the problems. The FDA took action to change the labeling on estrogen in the face of citizen and medical experts’ pressure; it should do more now to demand transparency from patch manufacturers.
Most importantly, it is on all of us to call out the cracks in the current system. Instead of repeating “there’s a patch shortage” or a “surge in demand,” say that a shockingly small minority of menopausal women still even get hormonal treatments prescribed at all, and three drug companies control the vast majority of claims in this country. Those are the real problems that need real solutions.
Jennifer Weiss-Wolf, the executive director of the Birnbaum Women’s Leadership Center at New York University School of Law, is the author of the forthcoming book “When in Menopause: A User’s Manual & Citizen’s Guide.” Suzanne Gilberg, an obstetrician and gynecologist in Los Angeles, is the author of “Menopause Bootcamp.”
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