For decades, juvenile hormone (JH) has been studied in the context of the evolution and regulation of dispersal polymorphism, most notably wing polymorphism in insects. The first part of the talk will briefly review the state of the art regarding JH regulation of dispersal polymorphism, focusing on both regulation of morph development, and the trade-off between flight and reproduction in adults. The major part of the talk will focus on a newly discovered JH titer circadian rhythm polymorphism (presence or absence of a cycle) that is strongly associated with wing polymorphism in the cricket, Gryllus firmus. The characteristics of this surprising circadian polymorphism in lab and field populations, its underlying causes, and functional significance will be discussed.