Screwworms are the flesh‑eating maggots (larvae) of certain parasitic flies that invade living tissue of warm‑blooded animals—and sometimes people—causing a serious disease called myiasis.

What screw worms are

  • “Screwworm” usually refers to the New World screwworm fly, Cochliomyia hominivorax , a type of blowfly.
  • The name comes from the screw‑like body and the way the maggots spiral deeper into flesh as they feed.

How they infect

  • Adult flies are attracted to open wounds or body openings (nose, eyes, mouth, genitals, umbilical cord of newborns) on live, warm‑blooded animals.
  • A single female can lay hundreds of eggs on a wound; these hatch into larvae that burrow into and eat the living tissue, enlarging and deepening the wound.

Why they’re dangerous

  • The feeding larvae cause severe pain, tissue destruction, foul‑smelling lesions, and can be fatal if not treated promptly.
  • Screwworms mainly affect livestock and wildlife but can also infest humans, making them an important public‑health and agricultural threat.

Where they’re found today

  • New World screwworm is now mostly found in parts of South America and the Caribbean; it does not normally circulate in the continental United States, though imported or travel‑related cases can occur.
  • Because of the risk to cattle and other animals, countries maintain surveillance and rapid‑response programs to keep screwworm out or eradicate outbreaks.

If you’re worried

  • Any maggots in a wound on a person or animal—especially with increasing pain, swelling, or bad smell—should be treated as urgent: seek medical or veterinary care immediately.
  • Protection in endemic regions includes promptly cleaning and covering wounds, using insect repellent, and monitoring livestock for signs of infestation.

Information gathered from public forums or data available on the internet and portrayed here.