Stomach hair worm occurs commonly in sheep, goats and other ruminants, often in association with the brown stomach worm (Teladorsagia) but appears to be relatively harmless. This worm also occurs in horses.
Adult worms are very small (smaller than Teladorsagia), slender, hair-like and reddish-brown. Females are 5–8 mm and males 4–7 mm long. Heavy burdens (40–70,000 or more worms) may exacerbate inflammation of the fourth stomach caused by Teladorsagia. The seasonal pattern of larval availability on pasture is similar to that for Teladorsagia.