Also called black-legged ticks, deer ticks are common in woods and grassy areas of the Northeast and northern United States. Reddish-brown adults like the one shown here are only one-eighth of an inch long. Tiny immature ticks that are about the size of a poppy seed also bite. Deer ticks infected with the bacteria Borrelia burgdorferi can cause Lyme disease in people, dogs, and cats. You might not even notice the tick or its bite. But if you do, remove the tick within 48 hours to limit your chances of getting Lyme disease.