Ixodes scapularis

Deer or Blacklegged Tick

The blacklegged tick is of greatest importance to Midwesterners because it can transmit bacteria that cause Lyme disease (Borrelia burgdorferi). 

The blacklegged tick is a three-host tick (feeding on three different host individuals during its lifetime) completing its life cycle in two years in most of the Midwest. Adults are active during the spring and fall. Nymphs and larvae are active during early and late summer, respectively. Eggs hatch in the spring or summer.

Adults and nymphs of blacklegged ticks generally have black or dark brown legs, mouthparts, and backs. Both larvae (about 0.8 mm) and nymphs (about 1.6 mm) are small and difficult to detect. The most commonly found are adult females, which when unfed are only slightly larger than a sesame seed (about 3.5 mm). Males are usually smaller (about 2.6 mm).

The seed ticks (larvae) climb short distances from the ground to wait on plants (questing) so they can attach to a passing small animal (usually mice) to feed. After feeding, larval ticks drop from the host and develop into nymphs. Nymphs will bite almost any mammal including humans, birds, or reptiles. Adults attach to a final host, usually larger mammals like deer, dogs, raccoons, foxes, or humans. After mating and feeding, adult females drop from the host, lay eggs, and die.

If a larva or nymph feeds on an animal infected with Lyme disease bacteria, it can be infected and can pass the bacteria to other animals as it feeds during its next stage. Nymphs are the real villains for humans in the Lyme disease infection cycle. They are so small that people may not know they have been bitten until the ticks have been attached for 36 hours – the minimal amount of time for transmission to occur in most cases.

Seasonal Activity of the Blacklegged Tick

Seasonal abundance of the three active life stages of the blacklegged tick in Iowa are presented as a percentage of total yearly submissions to Iowa's Lyme Disease Surveillance Program from 1990-2015. Numbers of blacklegged ticks infected with the Lyme disease bacteria are highest in May and October for adults, and in June for nymphs. Nymphs are most likely to transmit the Lyme disease agent to people. Seasonal abundance of ticks varies somewhat by state across the Midwest, but is similar to the pattern shown here.

Videos of questing blacklegged ticks

To find a host from which to take a blood meal, tick larvae, nymphs, and adults climb leaves and sticks, extend their front legs, and wait for potential hosts to come by. Heat, movement, and other signals like carbon dioxide given off by host animals cause the ticks to move quickly onto the passing host. These amazing videos by Dr. Graham Hickling at the University of Tennessee Center for Wildlife Health show questing blacklegged ticks. The different videos show both sexes and different life stages.