The threadworm, also called the pinworm, is a small, thin parasitic roundworm — Enterobius vermicularis — that infests the human large intestine, particularly in children. The female worms emerge at night to lay eggs around the anus, causing the intense itching that is the classic symptom; scratching transfers eggs to fingers and bedding, and the eggs spread easily within households. Infections are unpleasant and disruptive to sleep but rarely dangerous. Diagnosis is by finding the eggs with adhesive tape pressed to the skin, and treatment is with antiparasitic medicines given to the whole household. Hygiene — handwashing, short nails, hot-washing bedding — breaks the cycle of reinfection.