Friday Parasite #45: The Itch

This is the mite Sarcoptes scabiei. It's a human parasite, but unlike the other parasitic arachnids that bedevil people, it's a really little guy -- only about 400 micrometers long. So it's nearly impossible to see when it crawls onto you and starts hiding in your hair follicles and digging tunnels under your skin. Within a few weeks the tunnels turn into the severely itchy rash we call scabies.