There are over 650 different types of leeches, and most want to suck your blood These real-life vampires are nocturnal, like dark places, and only come out when they get thirsty. But can these bloodsuckers actually help humans? The ancient Egyptians may have been on to something. Readers learn about the habitats, history, and medical uses of the bloodsucking leech. Full-color photographs offer an up close view of these thirsty worms, and fact boxes share more details about their fascinating lives.