Blacklegged (deer) ticks

Identify blacklegged ticks from American dog ticks. Also learn how their appearance changes during and after feeding.

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Figure 1

Two unfed adult blacklegged ticks and two unfed adult American dog (wood) ticks on a ruler.

This figure shows the size and pattern of:

  • unfed adult blacklegged ticks (top row)
  • adult American dog (wood) ticks (bottom row)

American dog ticks are larger than blacklegged ticks:

  • female American dog ticks are about 0.5 cm long
  • female blacklegged ticks are about 0.3 cm long

The back of American dog ticks has a unique pattern, while the back of blacklegged ticks is not patterned.

Figure 2

Four unfed blacklegged ticks at different life stages on a dime.

This figure shows the life stages of a blacklegged tick that has not fed:

  • larva (1)
  • nymph (2)
  • adult male (3)
  • an adult female (4)

Figure 3

Five female blacklegged ticks, on a ruler and beside a dime, at different stages of feeding.

This figure shows 5 female blacklegged ticks in different stages of feeding.

Unfed female ticks are dark reddish-brown. They:

  • become paler brown to yellow as they start to feed
  • become greyish as they continue to feed
  • are dark grey-brown when fully fed

As they feed, the tick's stomach gets bigger. The tick grows from approximately 0.3 cm when unfed to 0.6 cm when partially fed.

When fully fed, the tick is:

  • about 1cm long
  • egg-shaped

Figure 4

Three nymphs of the blacklegged tick, on a ruler and beside a dime, at different stages of feeding.

Three nymphs of the blacklegged tick are shown in different stages of feeding.

The unfed nymphal ticks are:

  • very small (0.15 cm long)
  • grey-brown in colour

As they feed, their stomach grows and gets darker. When they are fully fed, the nymph is:

  • about 0.3 cm long
  • almost black in colour
  • egg-shaped
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