In 1996 the Center for Disease Control created the first map depicting cases of Lyme in the U.S., each indicated by a black dot. Regions on the east coast were solid black stretches, and areas on the Minnesota-Wisconsin border were heavily dotted. Eighteen years later, dots make their way further inward from the coast line and also envelop much of the Midwest. A new book investigates how and why tick populations are expanding and tick-borne illnesses such as Lyme disease are affecting a mass amount of the populationa. We talk to the author.