The human body louse exists everywhere people do, but usually only gets a foothold on people who do not have regular access to bathing facilities and clean clothing. They generally live in clothing, climbing down to the skin to feed on blood several times day. Adult lice are about the size of a sesame seed.
Interestingly, the term "nitpicking" came from the act of looking through a person's hair for the tiny eggs (nits) of lice and removing them one by one.
I managed to give myself a nightmare with this sketch! I dreamt that I had all these huge lice attached to me and my clothing, and I kept trying to get them off and hide them so other people wouldn't see. It was soooo freaky and not cool.[link]