This grasshopper met a gruesome end when a long, wriggly horsehair worm burst from its body! These worms are parasites that live inside hosts, like insects. They grow longer as they feed on the host’s innards. Most horsehair worms reach 5 to 10 centimeters (2 to 4 inches) long. But some species can grow as long as 0.6 meters (2 feet)!
The parasite’s life cycle begins when a female worm releases millions of eggs into water. Larvae hatch from the eggs. An aquatic insect or a crustacean eats one of these developing worms. The parasite matures inside its host. Then the worm bores a hole through the animal’s hard outer exoskeleton and exits through it and into the surrounding water. There it mates, and the cycle starts over. But how did a water-dwelling horsehair worm end up inside this grasshopper, which lives on land?
A grasshopper can ingest the parasite by drinking larvae-infested water. Once the larva develops into an adult worm, it needs to relocate to water to reproduce. So the parasite releases a chemical that affects the grasshopper’s brain, making it do something it normally wouldn’t: seek out water and dive in.
Adult horsehair worms live in just about any body of water, from lakes to puddles. “It gets its name because it can be found floating in troughs, where it’s mistaken for horsehair,” says Jeff Hahn, an entomologist who studies insects at the University of Minnesota. The worms are harmless to people, farm animals, and pets, says Hahn. But they’re an insect’s worst nightmare.