The Deer, Blacklegged and Bear Tick

Common Name:
Deer/Blacklegged/Bear Tick
Scientific Name:
Lxodes scapularis Say


The common name blacklegged refers to their dark legs which are in contrast to the paler body and that of deer because the preferred adult host is the white- tailed deer; in the midwest, it is called the bear tick. This tick is of medical importance because it is an important vector of Lyme disease. Blacklegged ticks are found primarily in the northeastern, Midwestern, and southeastern states in the United States, but extend into Mexico. In error, this tick was described in 1979 as the new species Ixodes dammini by Spielman, Clifford, Piesman & Corwin; this error was corrected by Olivier, Jr., et. al. in 1993.


Unengorged female about 1/8" (2.7 mm) long, male smaller (about 1/16"/2 mm). Body oval, dorsoventrally flattened (top to bottom), not hard-shelled. Color orangish brown except legs, mouthparts and scutum (dorsal shield just behind mouthparts) dark reddish brown but abdomen darker when engorged; male body reddish brown overall. Scutum present, longer than wide, almost completely covering dorsum in male. Eyes lacking. Capitutum (mouthparts and their base) visible from above; hypostome (toothed median mouthpart) with apex sharply pointed. Coxa I (I st pair of legs) with internal spur (projection from coxal base) overlapping coxa 11 (2nd pair of legs). Abdomen with anal groove in front of anus; lacking abdominal festoons (rectangular areas divided by grooves along posterior margin).

Unengorged lst instar larvae about 1/32" (0.7-0.8 mm) long, with 6 legs; 2nd instar nymphs about 1/1 6" (1.1 -1.8 mm) long, with 8 legs.


  1. Pacific/western blacklegged tick (Ixodes pacificus) with scutum (dorsal shield) almost round (subcircular);
  2. Other ixodid ticks (non-lxodes) with anal groove either behind anus, indistinct, or absent, festoons often present;
  3. Soft ticks (Argasidae) lack a scutum (dorsal shield), with capitulum (mouthparts and their base) ventral, not visible from above.


Although the life cycle (egg to egg) can be completed in 2 years in nature, it may be extended to 4 years if hosts are scarce. Adult ticks feed during the winter primarily on the white-tailed deer, Odocoileus virginianus (Zimmermann). Here they mate, with the male dying shortly after mating and the female remaining on the host. In the spring, the female drops off the host and deposits about 3,000 eggs. The 6-legged larvae hatch out in several weeks (48-135 days) and can be found June through September. They feed for 3-9 days but only once, usually on small mammals such as mice, chipmunks, voles, etc. but the preferred larval host is the white-footed mouse, Peromyscus leucopus Rafinesque. Larvae feeding before September molt promptly and overwinter as 8-legged nymphs; those which feed later, overwinter engorged and molt into nymphs the following spring. Nymphs feed for 3-8 days but only once during the summer, usually on mice or larger mammals such as squirrels, raccoons, opossums, skunks, dogs, and humans, or on birds. Nymphs can be found from April through August, with the population usually peaking in June or July. These fed nymphs then require 25-56 days to molt into adults in the autumn. The adults attach primarily to the white-tailed deer, engorge, and mate. The male dies after mating but the female continues to feed until egg development is completed and remains on the deer until spring when she drops off to lay eggs. Shortly after her eggs are laid, the female dies.

If adults do not feed during their first season (autumn through spring), they die before summer's end. If nymphs do not feed their first season (summer), most die off but they can survive through 2 seasons (May through August of the next year); they develop into adults in the same year in which they feed. Unfed larvae survive less than one year, they usually survive the winter but die during the following year.

Lyme disease is caused by the spirochete, Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner, which is a corkscrew-shaped bacteria. Its primary wild reservoir is the white-footed mouse which is infected by the spring-feeding, pathogen- infected blacklegged/deer tick nymphs. These white-footed mice then serve to infest the later-feeding blacklegged/deer tick larvae, which keeps the disease cycle going. Tick eggs don't contain the spirochete, so it is acquired via feeding.

It is the pathogen-infected blacklegged/deer tick nymphs, which are most active in mid-summer (May-July) and use a wide variety of hosts, that are primarily responsible for Lyme disease in humans in the northeast and midwest. Larvae and nymphs have been collected on 29 species of mammals in 7 orders, and from 49 species of birds (23 species being migratory birds) in 17 different families.

In the west, the primary Lyme disease vector is the Pacific/western blacklegged tick, lxodes pacificus Cooley and Kohis, while in the south the vector(s) is suspected to be the lone star tick, Amblyomma americanum (Linnaeus).


Blacklegged/deer ticks climb grass and shrubs to wait for a passing host, and move very little laterally. They concentrate on such vegetation located in transitional areas/zones such as where forest meets field, mowed lawn meets unmowed fence line, a foot/animal trail through high grass or forest, etc. Because these transitional areas or edge habitats are where most animals travel sometime each 24-hour period, this is where the ticks are mostly likely to acquire a host.

The other habitat most likely to harbor ticks is the den, nest, or nesting area of its host such as that of skunks, raccoons, opossums, but especially the white-footed mouse. The white-footed mouse prefers woody or brushy areas. It nests in any place that gives shelter such as below ground, in stumps, logs, old bird or squirrel nests, woodpiles, buildings, etc.

A favorite feeding area for these ticks on humans is at the back of the neck, at the base of the skull; long hair makes detection more difficult. However, the ticks will usually wonder about for up to 4 hours or so before they attach. Then, a tick has to be attached for a period of 6-8 hours before a successful transmission can take place.