Horsehair Worm
Scientific Name: Nematomorpha (various genera and species, e.g., Gordius)
Order & Family: Order: Nematomorpha (sometimes treated as a phylum); Family: Gordiidae (for horsehair worms)
Size: Typically 10 cm to 100 cm (4 inches to 3 feet) in length, but can be much longer, resembling a fine piece of thread or hair.
Natural Habitat
Adults are free-living in aquatic or semi-aquatic environments (streams, puddles, ponds, ditches, water troughs); larvae are internal parasites of arthropods, typically insects like crickets, grasshoppers, cockroaches, and beetles.
Diet & Feeding
Adult horsehair worms do not feed; they live off nutrient reserves accumulated during their parasitic larval stage. Larvae are endoparasites, absorbing nutrients directly from the hemocoel (body cavity) of their arthropod host.
Behavior Patterns
The most striking behavior is the manipulation of their host. When the parasitic larva is mature, it induces its terrestrial host to seek out water, where the adult worm emerges. Their life cycle begins with eggs laid in water, which hatch into larvae that are ingested by or penetrate an invertebrate host. Once mature, they emerge from the host, often killing it in the process.
Risks & Benefits
Horsehair worms pose no known direct risk to humans, pets, or livestock, as they are specific to invertebrate hosts. They do not sting, bite, or transmit diseases to vertebrates. From an ecological perspective, they act as a natural control for certain insect populations, particularly orthopterans (grasshoppers, crickets).
Identified on: 11/29/2025