Western blacklegged tick (Ixodes pacificus) surveillance

Estimated distribution of areas where the Western blacklegged tick (Ixodes pacificus) could survive and reproduce (yellow), and counties where established populations have been documented (red). Counties classified as “established” are those where six or more I. pacificus of a single life stage or more than one life stage of the tick were collected in the county within any 12-month period.  Counties not classified as established should not be interpreted as the tick being absent.

Western blacklegged tick (Ixodes pacificus) lifecycle

Ixodes pacificus typically lays eggs in the spring. These hatch into larva in the following spring. During the summer, larvae feed and then molt into nymphs the following spring. During the summer, nymphs feed and then molt into adults over the winter. Adults females will seek a winter or spring blood meal before laying eggs in spring, completing the lifecycle.

The lifecycle of Ixodes pacificus ticks generally lasts three years. During this time, they go through four life stages: egg, larva, nymph, and adult. After the eggs hatch, the ticks must have a blood meal at every stage to survive. Blacklegged ticks can feed from mammals, birds, reptiles, and amphibians. The ticks need a new host at each stage of their life.