Dr. Siddall's research focuses on the evolution of leeches and their blood-feeding behavior, as well as on protozoan parasitology in general. Dr. Siddall analyzes the evolutionary patterns of both blood-feeding and non-blood-feeding leeches to determine how they have managed to circumvent the blood-clotting mechanisms of their hosts. Knowledge gained from this research may be used one day to develop anti-coagulants and tumor inhibitors in humans. He also studies the evolutionary relationships of various protozoan groups - including some that threaten the oyster populations along the Atlantic Coast, and others that cause malaria and giardiasis. Currently, Dr. Siddall and colleagues are completing a project that establishes the origins of relationships among bird, lizard, human, and primate malarias. Another aspect of his work assesses the genetic diversity of leeches in wild populations decimated by centuries of over-exploitation, to determine their species' level of endangerment.