thoroughly spooked. With everything that can get you out here, what's the
point?" Mark is here to collect fresh specimens of H. ghilianii. Why? Well, even though these animals feed exclusively on it, blood alone is not able to sustain them; it lacks certain essential amino acids and vitamins. To make up for this deficit, bloodsucking leeches have evolved symbiotic relationships with special kinds of bacteria, which live in organs called mycetomes attached to the leech's esophagus. In exchange for a safe place to live, the microbes contribute the missing nutrients, Mark believes. He also suspects that H. ghilianii hosts a unique group of bacteria that provide this service, and he wants to find specimens (top) and look inside them (bottom). His work will help explain how such symbiosis evolved. By the way, check your legs—you might be fattening a giant Amazonian leech or two. Nothing like contributing to science, eh?