Dog ticks appear gray or green when they have become engorged with blood. Other North American tick species tend to be darker brown or black at all stages of their lives except for their engorged phase, when their abdomens lighten and expand.
Proper identification of dog ticks is important for assessing the risk of Lyme disease. Dog ticks are not the primary vector for Lyme disease. They are distinguished from deer ticks, which are considerably smaller and darker. Dog ticks are also distinct from lone star ticks, which also carry Lyme disease, as lone star ticks have an easily seen white spot on their scutum.