The long-range migration of insects in general is briefly discussed here and serves as an introduction for in-depth inquiry into the migratory ecology of Agrotis ipsilon, the black cutworm. Zoogeography, pest status and injury, and seasonal occurrence of the species are reviewed. Circumstantial evidence of long-range movement of A. ipsilon moths within both hemispheres is presented, followed by experimental evidence of long-range movement of A. ipsilon moths in China and North America. Based upon experimental evidence published by several investigators, a theory is proposed of the existence of a thermal range (0-36 degrees C) for A. ipsilon pupae that acts as the precursor for adult (moth) migration. This theory should help explain the circumstantial and empirical evidence gathered upon the annual appearance and disappearance of this species over large geographic areas.