The Blacklegged Tick

  • The blacklegged tick (or “deer tick”) is the smallest of these three dangerous hard ticks. It is also the primary carrier of:
  • Lyme disease
  • Human anaplasmosis
  • Babesiosis
  • Powassan virus

According to Purdue University’s Medical Entomology, the first in-state specimen of this tick was discovered (in the modern era) in northwestern Indiana in 1987. Since then, its habitat has expanded through, both:

  • Reproduction – a female will lay upwards of 3,000 eggs at the end of her three-year lifespan.
  • An extremely wide range of hosts – 57 species of birds, 41 species of mammals, and 11 species of lizards.

So, while its population is still most abundant in northwestern Indiana, it can be found in other parts of the state, as well.

The following table outlines some basic characteristics of the blacklegged tick:




Primary Host(s)

Most Active/Abundant Time Period Annually


About 1/32 in.

Light in the middle with a dark outer ring

White-footed mouse

July through September


About 1/16 in.

Dark in color

Small, ground-dwelling vertebrates; humans; pets

Late spring through early summer

Adult Male

A little less than 1/8 in.

Dark in color/ deep mahogany

Deer (for reproduction and feeding); pets; rarely humans

Late summer through fall, and again in early spring

Adult Female

A little more than 1/8 in.

Dark in color/ deep mahogany, with a significant light red stripe along the bottom of its scutum; more teardrop-shaped than males; longer mouthparts than males

Deer (for reproduction and feeding); pets; rarely humans

Late summer through fall, and again in early spring

Of all these stages, the nymphal stage tick is the most dangerous to humans, mainly because the nymph tick is roughly the size of a poppy seed. So, a person will rarely detect it until the tick has attached and fed on the human’s blood – which means the tick has already likely transmitted Lyme or another disease to the person.

For a quick reference ID card for identifying the blacklegged tick, the lone star tick, and the American dog tick click here.

For more information about various tips and strategies for preventing tick bites, visit our Prevention page.