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Deer Tick

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Life Cycle

Like all ticks in the genus Ixodes, I. scapularis is 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. scapularis may range from two to four years and appears to be regulated by host abundance and physiological mechanisms of the tick. Typically, I. scapularis takes 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 mates repeatedly with several females. The females then fall to the ground and lay up to 3000 eggs in soil and litter before dying. Eggs take about 1 month to hatch.
A second breeding period in the spring results from unengorged adults that have over wintered.

Figure 1: Adult male black-legged deer tick.
Figure 2: Adult female black-legged deer tick.

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 over wintered.
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 of the black-legged tick is about the size of a poppy seed, flat, six-legged, and nearly translucent, making it extremely difficult to see. 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.

Figure 3: Larva of the black-legged deer tick.

The nymphal stage, most responsible for disease transmission to humans, is about the size of a flat pinhead or sesame seed, eight-legged and translucent with a slight tinge of gray, also making it very difficult to see.
The 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 over wintered. Furthermore, there is a small amount of nymphal activity in the early fall, most likely developing from the early spring larvae.

Figure 1: Nymph of the black-legged deer tick.

Larvae and nymphs feed primarily on small mammals (especially the white-footed mouse, other rodents, and insectivores), and also on birds, dogs, deer, and humans. Nymphs aggressively bite humans.

   

Further information

  • Sonenshine DE: Biology of Ticks. Part 1, 1991, Oxford University Press, New York

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