Range of counties (a) with established I. scapularis or I. pacificus populations and (b) where host-seeking I. scapularis or I. pacificus nymphal or adult densities were reported per 1,000 m2, based on records reported to the Centers for Disease Control and Prevention’s ArboNET Tick Module prior to the National Tick Surveillance Program (pre-NTSP, 2004–2017) and during the NTSP (ArboNET, 2018–2023). Establishment is defined as 6 or more ticks of one life stage, or more than one life stage collected in a county in a calendar year. Density estimates (b) were included if at least 750 m2 sampling sites were drag or flag sampled during the expected peak of seasonal activity for each life stage. Unshaded counties represent either a lack of tick collection and/or testing records submitted to the NTSP, or records not meeting inclusion criteria.
