Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Head Lice ?
    ### Response:
    Head lice are parasitic wingless insects. They live on people's heads and feed on their blood. An adult louse is about the size of a sesame seed. The eggs, called nits, are even smaller - about the size of a knot in thread. Lice and nits are found on or near the scalp, most often at the neckline and behind the ears.
    