The tiny males have caudal alae and a single spicule. In the female the vulva is situated anteriorly. Oxyuris eggs are ovoid, yellow, and slightly flattened on one side with a mucoid plug at one end. Development is rapid, and the eggs develop through to the infective stage in 4 to 5 days. The infective stage is the egg, containing a third stage larva.
Infection then is by ingestion of eggs containing third stage larvae.
Eggs hatch in the small intestine and larvae pass into the large intestine, migrating into the crypts of the cecum and colon. Here development to L4 takes place, L4 emerge, feed on the mucosa, then mature to adult stages which feed on intestinal contents. Prepatent period is 5 months. Egg-laying female adults cause a perineal irritation, resulting in anal pruritis, causing infected horses to rub, producing broken hairs, bare patches, and skin inflammation of the skin over the rump and tail head. Diagnosis is based on signs of anal itching, finding egg masses on the perineum, and finding long-tailed females in feces of infected animals.