Tick Borne Disease Program
Black-legged Ticks (Deer Ticks) Ixodes scapularis
Life Cycle
Like all ticks in the genus Ixodes, I. scapularisis a three host tick. Each feeding stage (larva, nymph and adult) requires one vertebrate blood meal for its development. Each stage attaches to a vertebrate host, feeds to repletion, detaches, drops from the host (usually into the leaf litter) and molts to the next stage. The life cycle of I. scapularismay range from two to four years and appears to be regulated by host abundance and physiological mechanisms of the tick. Typically, I. scapularistakes about two years to complete one life cycle. The adults appear to exhibit two breeding periods. Adults, resulting from spring nymphs, emerge in the early fall and undergo a fall breeding period. While on the host animal (primarily white-tailed deer), the female tick feeds to repletion and the male tick mates repeatedly with several females. The females then fall to the ground and lay a cluster of one to two thousand eggs before dying. A second breeding period in the spring results from unengorged adults that have overwintered. There is a bimodal spring-summer distribution of larvae. The first larval activity peak is seen in May and results from females that successfully mated and deposited their eggs the previous fall and from unfed larvae that have overwintered. The second and much greater larval activity peak, seen in August, results from females that successfully mated and deposited their eggs earlier that spring. The larval stage is the only six-legged stage in the life cycle. They usually feed on small mammals for three to five days before dropping from the host to metamorphose to the nymphal stage in the leaf litter. The eight-legged nymphs are most active in the months of May, June and July. These nymphs have developed from larvae of the previous summer that have successfully fed and overwintered. Furthermore, there is a small amount of nymphal activity in the early fall, most likely developing from the early spring larvae.
Host Relationships
Ixodes scapularishas been reported from at least 125 different species of hosts. The adults appear to prefer medium to larger sized mammals and are only moderately host specific, as they have been recorded from at least 27 different mammalian and one lizard host species. The white-tailed deer (Odocoileus virginianus)is the most commonly infested mammalian species. Populations of I. scapularisappear most abundant in areas where deer are also numerous. However, adult deer ticks have also been recorded from black bears, Ursus americanus,in Wisconsin, opossums, Didelphis virginiana;raccoons, Procyon lotor,and skunks, Mephitis mephitis,in New York and woodchucks, Marmota monax;gray squirrels, Sciurus carolinensisand red fox, Vulpes vulpes.
Immature I. scapularisare less host specific. They have been reported from at least 41 mammalian, 57 avian species and 14 species of lizards. In some instances the immatures can be found on the same hosts as the adults; for example, both larvae and nymphs can be found on white-tailed deer. However, in most instances the immatures prefer smaller mammalian hosts, as well as ground-nesting and ground-foraging birds. The white-footed mouse, Peromyscus leucopus is an important host for larval I. scapularis. Other hosts, such as chipmunks (Tamais striatus)and meadow voles (Microtus pennsylvanicus),may serve as hosts to larval I. scapularis. Short-tailed shrews (Blarina brevicauda),southern red-backed voles (Clethrionomys gapperi),pine voles (Microtus pinetorum),eastern cottontail rabbits (Sylvilagus floridanus)and meadow jumping mice (Zapus hudsonicus)also harbor immature I. scapularis. Some common avian hosts include the gray catbird (Dumetella carolinensis),blue jay (Cyanocitta cristata),American robin (Turdus migratorius),Carolina wren (Thryothorus ludovicians)and common yellow throat (Geothlypis trichas). Other hosts (dogs, cats, humans, etc.) may be acceptable hosts for any of the three I. scapularislife stages. However, these hosts are usually accidental hosts and are not normally successfully parasitized.
Page Last Updated: 4/5/2016 2:58:00 PM