Fig. 1.

Distribution by county of recorded presence of I. scapularis and I. pacificus in the continental United States (a) 1907–1996 (from Dennis et al. 1998), (b) 1907–2015. Counties classified as established (red or green) for a given tick species had at least six ticks or two life stages recorded within a single calendar year. Counties with fewer ticks of a single life stage were classified as reported (blue or yellow) for the tick species. Counties shown in white indicate“no records.”