The western black-legged tick, Ixodes pacificus , is responsible for Lyme disease transmission on the pacific coast.
Ticks begin as eggs and hatch into the six legged larval form.
Larvae usually feed on small animals and birds, particularly the white footed mouse, which serves as a major reservoir for Borrelia burgdorferi . Larvae can acquire the spirochete while feeding on an infected host, and transmit it to subsequent hosts. Once the tick acquires the spirochete it will remain within the tick throughout its life cycle. However, female ticks do not pass the spirochete on to the next generation. Nymphs are more likely to feed on humans than larva.