Horsehair worm

Horsehair worms are long, slender parasitic worms in the phylum Nematomorpha, also called Gordian worms.

Horsehair worms are long, slender parasitic worms in the phylum Nematomorpha, also called Gordian worms. Their larvae develop inside invertebrate hosts such as insects, while adults are free-living in water or very moist places. They are harmless to people, pets, livestock, and plants.

Classification and names

Horsehair worms are members of the phylum Nematomorpha and are commonly called Gordian worms. The name refers to their hair-like appearance and the knot-like coils they often form.

Life cycle

The worms begin life as larvae inside arthropod hosts such as crickets and grasshoppers. After developing, the adults emerge into water or moist surroundings to mate and lay eggs. Some species influence host behaviour, causing insects to enter water so the worms can complete their life cycle.

Appearance and habitat

Adults are long, very thin worms, typically about 20–30 cm long and about 1 mm wide. They are often pale, though colours vary by species. They are usually found in wet or humid places, including streams, puddles, bird baths, damp soil, and even water troughs and toilets.

Ecological role

Horsehair worms are considered beneficial because they parasitize insects and other invertebrates. Their presence can reduce populations of some pest species. They do not harm humans, pets, livestock, or plants.