How often do periodical cicadas emerge in large numbers?

Periodical cicadas do not emerge every year; rather, they are known for their highly synchronized life cycles, appearing aboveground in massive numbers only every 13 or 17 years.1

These insects are categorized into regional groups called broods, which are designated by Roman numerals. Because there are 12 distinct broods of 17-year cicadas and 3 broods of 13-year cicadas, it is possible to find a brood of adult periodical cicadas emerging somewhere in the United States nearly every year by traveling to the appropriate location.1

While these emergences are highly predictable, they are not always perfectly synchronized across a species' entire geographic distribution, and some individuals may emerge a year early or late, a phenomenon known as straggling. Additionally, other types of cicadas, such as "harvest flies" or annual species, appear more frequently, with cycles ranging from one to five years.12