Pinworm

The human gastrointestinal tract, specifically the large intestine and rectum.

Intestinal contents and nutrients found within the human host's digestive system.

Nighttime activity where gravid females migrate out of the anus to lay thousands of eggs on the perianal skin, causing itching ('pruritus ani').

Risk: Causes Enterobiasis, a common parasitic infection leading to itching, restless sleep, and irritability. Ecosystem: No known benefits; strictly a human parasite.