Extension of the range of Dermacentor variabilis (Acari: Ixodidae) in Pennsylvania.

The American dog tick, Dermacentor variabilis (Say), until recently was recorded only from the southeastern and southwestern counties of Pennsylvania. Since 1968, this species has expanded its range and is reported from 63 of Pennsylvania's 67 counties. This range extension is a matter of concern to the medical community and to physicians throughout Pennsylvania, particularly those with practices in areas where this tick was previously unknown and who may not be familiar with the symptoms of Rocky Mountain spotted fever.