The three species groups are estimated to have diverged 3.9–2.5 million years ago (mya), and subsequent divergence of the present 13-year (mostly southern) and 17-year (mostly northern) life cycles has occurred in parallel in the three species groups during the Quaternary, except for the first split of the 13-year species, M. tredecim, in the Decim group (0.5 mya) (Fig. 1)6. The synchronisation of prolonged life cycles among species groups is thought to have evolved for a predation-avoidance strategy7, an ecological problem shared among co-occurring species. The divergence of 13-year and 17-year life cycles may have been related to adaptation to climatic changes across glacial cycles; the 4-year extension of juvenile stages may have been advantageous for surviving in cooler northern environments8,9.