Periodical cicadas often emerge in years before or after they are expected to emerge. When periodical cicadas don’t emerge on schedule we call them stragglers. Typically cicadas with a 17-year lifecycle will emerge 4 years early, and cicadas with a 13-year cycle will emerge 4 years late.
This image indicates the probability of Magicicada straggler emergences. Courtesy of cicada researcher Chris Simon.
People hear the word straggler and assume it means something that lags behind, but that is a laggard. Straggler simply means something that has deviated from an expected date/time. That said, periodical cicadas that emerge early can also be called precursors.
Visit Brood Chart to see when stragglers will be most likely.
Extremely likely stragglers in the next 10 years (or so):
2017: Brood X 4 years early.
2018: Brood XXII 4 years late.
2019: Brood XXIII 4 years late.
2020: Brood XIII 4 years early.
2021: Brood XIV 4 years early.
2025: Brood I 4 years early.