Pinworm

The human large intestine (specifically the cecum and appendix) and the perianal area during egg-laying.

Content of the human intestine and epithelial cells.

Nocturnal activity; gravid females migrate out of the anus at night to deposit eggs on the skin of the perianal area, causing an itchy sensation (pruritus ani).

Risks include intense itching, sleeplessness, and potential secondary bacterial infections from scratching. They provide no ecosystem benefits and are considered a common human parasite, particularly in children.