We're surrounded by unseen worlds as complex and densely inhabited as the largest cities. Take a tour through two of these minute metropolises: Dust mites have taken over your home. Don't think so? If you examined your pillow under a microscope, you'd find it to be three-quarters cotton and one-quarter dead and living bugs! High above in the forest canopy, the wildlife's really swinging - and we don't just mean the monkeys. Meet the fungi, insects, and other tiny denizens that truly rule this roost.