Life history diversity is a remarkable feature of living organisms and underlies fundamental evolutionary questions1. Periodical cicadas of the genus Magicicada are found only in the eastern United States and are well known for their unusual life history patterns, characterised by prolonged juvenile periods of 13 or 17 years, followed by synchronised mass emergence of adults within local populations2. Only one cohort, or ‘brood’, of periodical cicadas emerges every 13 or 17 years in any given location. There are three co-occurring species groups of periodical cicadas, Decim, Decula and Cassini. Each has one species with a 17-year life cycle and one or two species with a 13-year cycle, and there are seven described species (four 13-year and three 17-year) in total3,4,5 (Fig. 1). Although the species groups clearly differ in morphology, male songs and female song preferences, the 13-year and 17-year species within each species group are extremely similar or indistinguishable in these characters4,5; thus, the difference in life cycle length is one of the only diagnostic characters for their identification.