The ticks that generally transmit Rocky Mountain spotted fever are large ticks: American dog tick [Dermacentor variabilis], Rocky Mountain wood tick [D. andersoni]. These are large ticks, in contrast to the small ticks (Deer tick [Ixodes scapularis], Pacific Black-Legged tick [I. pacificus] that generally transmit the spiral-shaped bacterium that causes Lyme disease. However, the larger Lone star tick [Amblyomma americanum] is capable of transmitting both diseases.