Oecanthus forbesi and Oecanthus nigricornis are morphologically indistinguishable but separable on the basis of their calling songs. Dots show county records of O. forbesi that are based on tape-recorded males. East of the shaded area, tapes of males of nigricornis/forbesi morphology have proved to be O. nigricornis except for one record from eastern New York. West of the shaded area, no forbesi males have been taped.