Meet the New World screwworm. Sounds like a metal band. Acts like a horror movie. This fly does not wait for you to die. Its babies prefer living flesh. Yes, yours. Or your dog’s. Or a newborn calf’s. The Latin name even translates to “man eater.” Cozy.
A recent Maryland case put it back on the U.S. map. The infection was travel associated and linked to the wider Central America and Mexico outbreak. Public health officials say the risk to the general public remains very low, but the cringe factor is off the charts. Meanwhile, Mexico just reported a bovine case in Nuevo León close to our border, which has both countries on alert.
How it actually works
The adult new world screwworm fly smells an open wound. She lands. She lays. Within hours the eggs hatch. The maggots burrow inward and eat as they go. The wound enlarges. More flies arrive for the all-you-can-eat buffet. After about a week, the larvae drop out and pupate in the soil. A new fly climbs back into the world days to weeks later, timing set by heat and humidity. Nature, you are creative and rude.
Odd and awful facts you cannot unsee
*Female screwworms are basically monogamous. One mate for life. Weirdly wholesome, except for the flesh eating part. This quirk let scientists design a control program that changed history.
*The name “screwworm” comes from the way the larvae twist into flesh like a tiny corkscrew. They have ringed bodies with little backward spines and evil looking mouth hooks. Charming.
*One female can lay roughly 200 to 300 eggs at a time. She often picks the edge of a wound or a moist opening. The umbilical stump of newborn animals is a favorite. Eggs can hatch in as little as 12 hours.
*These maggots prefer healthy living tissue. Not the rotting stuff most flies like. Again, rude.
The science that beat it once
Backstory time. In the mid 20th century, U.S. scientists built a program that mass reared screwworm flies, sterilized the males with radiation, then released them in ridiculous numbers. Females mate once. If she mates with a sterile male, no viable babies. Do that at scale and the population collapses. It worked so well the parasite was eradicated from the U.S. by 1966 and pushed south to a permanent barrier at the Darién in Panama. Florida’s 2016 outbreak in Key deer was cleaned up with the same strategy.
Why you are seeing it in headlines again
Central America and Mexico have had a resurgence in animals, which creates spillover risk through travel, trade, and wildlife movement. The U.S. and Panama maintain a joint barrier program and the USDA is now building out new sterile fly capacity in Texas to harden the border. We are talking hundreds of millions of sterile flies per week when needed. I know. That is a lot of flies. It is also how you keep a flesh eater out.
What to watch next
*More sterile fly releases along the border if Mexico’s northern cases tick up.
*Vet alerts asking ranchers and pet owners to examine any wound that will not heal or that looks unusually wet, painful, or wriggly. (You are welcome for that visual.)
*Quick responses to any U.S. detection. We have the playbook. We have the flies. We like our skin.
Quick Bits
*Can people catch it here from the air. Not how it works. The fly needs an open wound and warm bodies. The current U.S. risk is very low, and control programs are active. If you have a travel wound that is not healing, go be seen. #don’tbeahero. CIDRAP
*How do I protect pets. Keep wounds clean and covered. Check after outdoor play, especially nose, ears, tail base, and any hot spots. If you see a moving white rice party in a wound, do not Google at 2 a.m. Call the vet. Texas Farm Bureau
*Why “man eater.” Because the species name hominivorax means exactly that. A biologist with a sense of theater named it. Tellus
If you have a screwworm story and you are willing to talk about it, email me. If you are a USDA or COPEG scientist, come on Causes or Cures and tell us how you plan to outfly a parasite. I will bring curiosity and coffee. You bring the sterile flies.
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Other gems from WTF NEWS Section:
Malaria in New Jersey? A Weird Comeback Case
How a Woman in Texas Died from Her Sinus Rinse
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