The changing face as the deer tick engorges
Left to Right: unengorged female, 1/4 engorged, 1/2 engorged and fully engorged.
Note the circular dark spot above the mouthpart . . . this is the shield. The shield does not change as the tick engorges and it is the key component, along with mouthparts in identifying different ticks. Because the engorged deer tick is often confused with the brown dog tick, you should closely compare the two species. Although the shield appears dark and similar in shape the shorter mouthparts of the brown dog tick are easy to identify. Brown dog ticks seldom attack humans.
Image courtesy of Dick Gadd, SCS Limited