Pinworm

The human large intestine; eggs are commonly found in household dust, bedding, and clothing.

Content of the human host's digestive tract and epithelial cells.

Adult females migrate out of the anus at night to lay thousands of eggs on the perianal skin, which causes intense itching.

Risks include perianal itching (pruritus ani), disturbed sleep, and potential secondary bacterial infections from scratching. They provide no known benefits to humans.