The 2018 periodical cicada emergence is over.
If you are seeing cicadas in July, August, or September, you are seeing “summer” or “Dog Day” cicadas. Some individuals in each of these populations come out each year, and they are not periodical.
Periodical cicadas are unique in that all (or nearly all) members of the population emerge in one year and then are absent in the intervening years.
Periodical cicada Brood VII emerged in upstate New York, south of Syracuse, in June 2018. Although this brood has undergone a severe decline over the last few generations, some extremely dense populations remain, especially in and around the Onondaga Nation. Among 17-year broods, four-year late Brood III stragglers may have emerged in Illinois and Iowa, but since Brood XI is extinct, no four-year early Brood XI stragglers are expected. Among 13-year broods, four-year late Brood XXII stragglers may have emerged. No four-year early 13-year cicadas were expected.