No one wants to talk about – or even think about – flesh-eating parasites.

That said, isn’t it better to know and maybe able to take steps to maybe not encounter them in real life?

Because according to researchers, we might need that information in the near future.

The New World Screwworm (NWS) fly larvae experienced a resurgence in Costa Rica in early 2024, sparking a national emergency. And recently, it has been found in at least one cow in southern Mexico. From there, it’s only a short skip into the southern United States.

It’s been 34 years since the NWS has been documented in Mexico, and almost 60 years since it’s been found in the United States.

The Wildlife Conservation Society of Mesoamerica’s Regional Director, Jeremy Radachowsky, issued a statement about the situation.

“Illegal cattle trade in Mesoamerica, the southern border of North America extending to the Pacific coast of Central America, follows transboundary routes starting in Nicaragua and passing through Honduras and Guatemala, before infiltrating Mexico’s food supply chain and reaching as far as the US.”

There is some precedent for how quickly something like this could potentially move.

“This unregulated cross-border movement has created a rapid corridor for the parasite, allowing it to travel nearly 700 miles from the Nicaragua-Honduras border to Catazaja, Mexico – in just two and a half months.”

The Texas Parks and Wildlife Department has issued a statement warning residents to be vigilant for signs of NWS infections, like irritated/depressed behavior, loss of appetite, head shaking, a smell of decaying flesh, larvae in wounds, and self-isolation from animals and other people.

There are two species of screwworms, both of which are obligate parasites during the larval stage. The New World screwworm, also known as a “true screwworm,” is indigenous to a lot of North and South America.

They prefer to lay their eggs on the wounds of living animals as opposed to carrion – and one clutch contains between 100 and 350 eggs. They hatch in less than 24 hours, and immediately burrow downward into the wound, and their scent attracts more egg-carrying females to the same wound.

This means an infection can spread rapidly.

The larvae grow to a size of about 0.6 inches in a week, and then stop feeding and fall to the ground to burrow and pupate. They emerge between 7 and 60 days later to continue the cycle again.

Infestations are complicated by the increased chance of different larval fly species entering the wound, which increases the chance of infection.

Untreated infections are fatal in 1-2 weeks.

This all sounds very scary, but the US Department of Agriculture has extremely successful tactics for keeping the population under control. This is known as the sterile insect technique (SIT), which sterilizes millions of captive male NWS using radiation. The males are then inserted into wild populations, and since females only mate once during their lifespan, this method is very effective in eradicating the NWS in a short period.

This was first used in 1958 in the United States, when infestations were decimating livestock in Florida. It has been used since then to control outbreaks in the Americas, and has been parlayed into eradicating other invasive species, too.

Right now, the Panama-United States Commission for the Eradication and Prevention of the Cattle Screwworm (COPEG) are monitoring and maintaining the Permanent Prevention Biological Barrier to keep the NWS populations under control.

Until that time, experts say that if you live in the southern United States, especially in areas that border Mexico, to make sure to wear insect repellent and cover any open wounds while outside.

Because those symptoms definitely don’t sound like the way you want to go.

Thought that was fascinating? Here’s another story you might like: Why You’ll Never See A Great White Shark In An Aquarium