These long, active worms may be observed during late summer or fall in streams and ponds, but are more commonly noticed in domestic water containers such as bird baths, swimming pools, water troughs, pet dishes, sinks, bathtubs and toilets. They may also be found on damp garden soil or vegetable plants after a rain. Amazingly, the entire horsehair worm grew and developed as a parasite inside the body cavity of crickets and other large insects such as grasshoppers, katydids, beetles and cockroaches. This internal parasite of insects does not harm humans, animals or plants.
Parasitized crickets are thirsty and go to water to drink.
While there the horsehair worm emerges from the insect's body and swims away in the water, an essential step in the life cycle of this internal parasite. Insects infected with horsehair worms die as a result of the parasite. Horsehair worms are white when they first emerge from the host's body. Another name for horsehair worm is Gordian worm. Horsehair worms resemble hairs from horses actively moving in the water.