Millions of years ago, ancient flies evolved to feed on the blood of vertebrates, becoming the mosquitoes that bite us today. This behavior profoundly altered the health and history of humans by transmitting numerous disease-causing pathogens. Trevor Sorrells studies the neural circuits in the mosquito brain that control how mosquitoes locate a source of blood. By identifying these neurons and comparing them across insects, we can understand the evolutionary origins of this innovation in behavior and develop new strategies to prevent the spread of mosquito-borne illness.