Enterobiasis is the common children’s disease caused by threadworms — pinworms — in the large intestine. Enterobius vermicularis is a small white nematode; the female migrates to the anus at night to lay eggs, causing the intense itching that is the disease’s signature, and the eggs spread via fingers, bedding, and dust to reinfect. It is more nuisance than danger — the worms do not invade tissue — but the itching disturbs sleep and the whole household usually needs treatment, since spread within families is the rule. Diagnosis is the sticky-tape test on the perianal skin; treatment is a single anthelmintic dose repeated after two weeks, plus rigorous hygiene — handwashing, laundering bedding, trimming nails. Threadworms are a reminder that the large intestine hosts passengers as well as flora.