Walk in the woods anywhere in the northeastern U.S., and you stand a good chance of encountering this arachnid freeloader. The blacklegged tick, Ixodes scapularis, is an ectoparasite best known for spreading Lyme disease.
Most people refer to this species as the deer tick, and believe deer to be the primary culprits in spreading Lyme and other infectious diseases. In truth, the white footed mouse is the primary carrier, infecting immature ticks with the bacterium. In the next life stage, the same tick may attach to a deer host, infecting the deer as well.
Adult blacklegged ticks are only the size of a sesame seed. Females have a black head and dorsal shield, and a dark red abdomen. Males are entirely black or dark brown. Not surprisingly, their eight legs are black. Under magnification, you may also observe the blacklegged tick's characteristic anal opening, which appears within a horseshoe-shaped ridge on the lower edge of the abdomen, on the ventral side. Adults can be active year-round, including winter, if temperatures remain above freezing. You are most likely to encounter adult blacklegged ticks during the fall and early spring.
Though they are only the size of a poppy seed, Ixodes scapularis nymphs are worth recognizing as well. At least 70% of Lyme disease cases result from the bites of ticks in the nymph stage. The blacklegged tick nymph has a dark head, but the body may appear translucent. Like the adult, the nymph has four pairs of dark legs. The best (or worst) time for becoming the involuntary host of a nymph is May or June.
As the expression goes, you probably wouldn't know a blacklegged tick larva if it crawled up and bit you. The larvae are about the size of the period at the end of this sentence, making them difficult to observe with the naked eye. Larvae live at ground level, and rarely come in contact with people. August is the prime month for larval activity.
Ticks are ectoparasites and obligate blood feeders throughout their life cycle. In each stage, they require a single blood meal to molt and develop to the next stage of life. Larvae typically feed on the blood of mice or birds. Nymphs and adult blacklegged ticks feed on larger hosts, including raccoons, deer, people, and pets. Immature blacklegged ticks may also attach to humans, but go unnoticed due to their tiny size.
Blacklegged ticks undergo four stages of development: egg, larva, nymph, and adult.
Eggs - Eggs hatch between May and September.
Larvae - Larvae are most active in late summer. Once it feeds, the larva molts and becomes a nymph.
Nymphs - The nymph remains dormant through the first winter. In spring, nymphs begin feeding, usually on larger mammals including humans. Nymphs feed between May and August.
Adults - New adult females may feed and mate in the fall; if they do not find a bloodmeal in the fall, they overwinter and wait until spring to feed. Males do not feed, but will attach to a host and look for a female mate on the host organism. Once the female lays eggs, she dies.
Special Adaptations and Defenses:
To penetrate and attach to a host animal, blacklegged ticks have specialized mouthparts visible when viewed dorsally. Slender stylets pierce the cell walls of host organisms, allowing the tick to feed on its blood. Once the tick has successfully penetrated a host, it produces a glue-like substance called attachment cement, which helps it stay in place for its bloodmeal. This makes an embedded tick tricky to remove. The idiosoma, a specialized region of the tick's body, expands during feeding to hold the bloodmeal.
Blacklegged ticks and other members of the family Ixodidae, the hard ticks, have a hardened plate called a scutum on the idiosoma region. The male's dorsal surface is covered completely by the scutum, restricting its ability to feed. The adult male does not feed at all, living only to mate.
Ixodes scapularis lives in moist, wooded areas where suitable hosts (mice, deer, dogs, humans) are found. Blacklegged ticks inhabit the understory of the forest and grassy open areas with high vegetation.
The blacklegged tick occurs in the eastern U.S., as well as parts of Mexico and Canada.