Mites and lice, fleas, ticks, and tapeworms -- most living creatures that have a habitat also are a habitat, including you (are you itchy yet?). Unwelcome guests -- parasites -- are everywhere, from the barnacles hitching a ride on a humpback whale's head to the tiny flies that control a bee's brain and make it literally dig its own grave. Now an expert team returns for an in-depth look at how these insidious critters do it, whether it's leaping aboard...