FRANCIS CHEE / SCIENCE PHOTO LIBRARY FRANCIS CHEE / SCIENCE PHOTO LIBRARY
Human head louse (Pediculus humanus capitis) on a human hair. The head louse is a small parasitic insect that lives its entire life in the hair on the head of humans. It drinks blood from the scalp, some of which is seen in its gut. An adult head louse may reach 3 millimetres in length. Infestation, called pediculosis, is very common and can cause an itchy scalp, but it is not medically significant. Nonetheless its eggs, called nits, are unsightly, and the condition is often targeted at schools.
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