" Deer ticks are small parasitic insects, barely visible to the naked eye, that feed off the blood of animals such as mice, squirrels, dogs, and even humans. Though their bites typically leave nothing more than an annoying bump, some ticks act as a vector for the often debilitating bacterial infection called Lyme disease. What Are The Symptoms of Lyme Disease? Lyme disease is a bacterial infection known to critically affect the skin, heart, joints, and ...