Air Date: Week of October 7, 2005

Living on Earth's Emily Togrimson reports on the hairworm, a parasite worthy of a grasshopper's worst nightmare.

Transcript

TORGRIMSON: An army of parasitic worms invades the bodies of grasshoppers, eats out their insides, and, like alien masterminds, brainwashes its hosts into mass suicide. Add a screaming blonde and green slime, and you’ve got a scene straight out of a B-grade sci-fi movie. But it’s also what a team of French scientists found when they studied the behavior of grasshoppers infected by parasitic hairworms.

Hairworms live inside grasshoppers, and they eat away at the grasshopper’s organs until only its head, legs, and body shell remain. The hairworm grows to three to four times the length of its grasshopper host. When it’s fully grown and ready to mate, it has just one problem – water. Hairworms must breed in water, so they ask – actually, they command – their host for one last favor.

The worms release proteins that affect chemical signals to the grasshopper’s brains. These proteins trigger a chemical reaction in the grasshopper’s central nervous system that makes the grasshopper turn zombie and plunge into the water. The worm exits the grasshopper’s drowning body through its rear and swims away to continue its life cycle.

This study suggests that bizarre behavior of parasite-infected animals is not just a coincidence of infection, but has an intentional effect. Scientists say further study of relationships between parasite and host might help researchers in the search for new drugs and vaccines. Until then, grasshoppers - watch your back. That's this week's Note on Emerging Science. I'm Emily Torgrimson.