The jump from the U.S. West Coast to the northeast states occured before 2009, by which time it had become abundant in New York's Central Park. The presence of the American Museum of Natural History, across Park Avenue, insured the scientific verification of its identity. The unique cerci of the male and the striking appearance of the early juveniles separate it from all other phaneropterines from the northern states. The abundance of photographers and Mediterranean katydids in the New York City area resulted in a flood of submissions to iNaturalist and BugGuide. The data from these web sites, arranged by Teresa Cooper, are here. County records represented by red dots on the map show how far the species has spread since 2009.
The northmost dot is a record by Brandon Woo, who found the species in Cambridge, Massachusetts, on 8 Oct 2017.