What are Screwworms? Why are they Dangerous
The New World screwworm is not actually a worm; it's the larval (maggot) stage of a metallic green blowfly called Cochliomyia hominivorax. What makes it so dangerous is that, unlike any other maggot that feeds on dead tissues, New World screwworm larvae feed on living flesh.
The adult fly doesn't eat flesh or bite animals; the problem is its babies. When female fly have to lay eggs it searchs for a living being with open wounds or cut, it lays eggs on the wound and the eggs hatch into larvae within a day which eats the flesh of the living being to survive, as they feed using their sharp mouth they borrow deeper into the wound making it larger and more painful, if left untreated it can cause infection and the infection can become severe and even cause death at some point.
After staying in the host's body for about a week, the larvae fall onto the ground, pupate in the soil and become a fly to continue the cycle.
Effect on Animals
Animals are the main victims of screwworms, especially cattle, sheep, goats, horses, pigs, pets and even wildlife. The screwworms use the body of a living being; hence, they don't mind what kind it is.
Screwworms make the wound bigger and even more painful than it initially was.
- It can cause severe bleeding and foul-smelling discharge from the wound.
- Cause weight loss in the animals.
- Cause difficulty in moving, depending on where the wound is located.
- Can cause weakness and reduce milk and meat production; it makes the animals weak, hence they produce less milk and meat.
Effect on Humans
Human cases are rare, but they can happen if a person has an untreated wound, or sometimes the eggs are laid in the nose, ear, eye, or mouth.
- Screwworms can cause intense pain and swelling.
- Bleeding and smelly, foul discharge from the wounds.
- The wound might grow larger instead of healing.
Humans are smarter than animals. If someone feels a movement in the wound, they should immediately go to the doctor instead of trying to remove it themselves. It can easily heal with proper medical care and rest, but if left untreated, it can cause severe infection, tissue damage and even lead to death.
Treatment
Screwworms can easily be treated if someone feels their wound isn't healing for days, feel a movement in the skin or suspect having a screwworm they should immediately go to a doctor instead of trying to remove it themselves, if removed themselves it can cause the wound to get bigger or screwworms to skim deeper into the skin, the doctor removes the larvae carefully, clean the wound and prescribed antibiotics if needed. We should not take risks in the matter of healthcare.
But for the animals in the wild, it might be problematic since they can't be treated; the larvae will grow in their flesh, and the animal will die eventually.
How the Screwworms were Eradicated
The New World screwworm was eradicated using one of the most successful pest-control programs ever developed: the Sterile Insect Technique (SIT).
In the 60's when the screwworms were causing trouble, scientists used this program.
Scientists didn't kill the screwworms; instead, they flooded the environment with sterile males.
The female flies only met once in their lives, so if they mated with the sterile males, the eggs became infertile, which caused their population to shrink till it was almost gone.
Why is it Returning
It never really disappeared from the world. After being eradicated from the U.S., the screwworm still existed in parts of South America and the Caribbean.
A barrier of sterile male flies was used in Panama to stop it from moving north.
The barrier began to fail around 2023. The flies gradually spread through Central America into southern Mexico, infecting wildlife, pets, and occasionally people.
It reached the United States. In June 2026, the first U.S. case in decades was confirmed in a calf in Texas. More cases followed, leading to quarantines, increased surveillance, and renewed releases of sterile flies.
How does it Impact Beef Prices?
Because of screwworms, farmers suffer heavy losses, meat supplies are disrupted, and food prices rise.
Cattle are screwworms' favourite hosts; if cattle become infected, they get weak, lose weight, produce less milk and produce very little meat. To prevent the screwworms from spreading, the U.S. have temporarily suspended the imports of live cattle, horses and some other livestock from Mexico. Due to fewer imported animals, the market doesn't have much beef; hence the prices of beef are touching the sky atp.
Government Decisions to Prevent Screwworms
Veterinarians and agricultural officials regularly check if any animal is wounded or has an infection; if any animal does have a wound or an infection, they get immediate treatment from professionals. The government has restricted importing animals from Mexico in order to reduce the risk of transporting Screwworms into different regions.
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