Western Black-legged Tick

Belonging to the family Ixodidae, the western black-legged tick is considered a slow-feeding hard tick which possesses a plated body armor. It is primarily found in the western region of the United States, particularly in northern California, and in western Canada. An adult male is around 2.54 mm in size, oval-shaped, and brownish-black in color. Due to the presence of a hard plate or scutum that completely covers the dorsal side of the male, they are unable to feed in large quantities. Therefore, males of this species are unable to become engorged. An unfed adult female is around 3.18 mm in size, has a brown-black scutum on the anterior back, an orange abdomen, and forward-projecting mouth-parts which enable feeding. While feeding, the adult female may engorge and expand to 9.5 mm or longer.

Ixodes pacificus is found in the western region of the United States and in western Canada. Although most prevalent in California, the tick has also been found in five other western states. These include Oregon, Washington, Utah, Nevada, and Arizona. I. pacificus has also been recorded in British Columbia.

The life cycle of Ixodes pacificus consists of four life stages: egg, larva, nymph, and adult. It takes approximately three years for the tick to complete its life cycle. Larvae, which emerge from eggs after approximately 53–55 days, take blood meals from vertebrates, such as lizards and birds. Protein from the blood meals, during the 4-10 day feeding period, enable the larvae to transform into immature nymphs after approximately 37–38 days. In order for the nymph to reach the adult stage, they continue to feed for 7–11 days on the blood of vertebrates. After 30 days, an adult tick emerges. Female adults will consume blood meals from medium and large-sized mammals, and then deposit eggs in areas of leaf litter or soil. Female adult ticks can deposit between 790 and 1,300 eggs over a period of 33–40 days.

Disease transmission. The western black-legged tick is a vector for Lyme disease, which is caused by infection with Borrelia burgdorferi. After feeding on a host animal infected with the bacterium, the tick is then able to transmit it to other animals, including humans, through subsequent blood meals. The nymphal stage, and sometimes adult female ticks, are responsible for the majority of transmission events. …