<P> These seven species are also sometimes grouped differently into three subgroups, the so - called Decim species group, Cassini species group, and Decula species group, reflecting strong similarities of each 17 - year species with one or more species with a 13 - year cycle . </P> <P> Note that while the original and correct spelling for Fisher's 17 - year species is cassinii, with two' i's, a large majority of publications have spelled the name cassini since the mid-1960s . However, the original spelling has been maintained throughout by taxonomic catalogues, and the rules of nomenclature support the priority of cassinii (Article 33.4). The correct spelling for the 13 - year relative is tredecassini . </P> <P> The 17 - year periodical cicadas are distributed across the eastern, upper midwestern, and Great Plains states within the U.S., while the 13 - year cicadas occur in the southern and Mississippi Valley states, but some may overlap slightly . For example, Broods IV (17 - year cycle) and XIX (13 - year cycle) overlap in western Missouri and eastern Oklahoma . Their emergences should again coincide in 2219, 2440, 2661, etc., as they did in 1998 (although distributions change slightly from generation to generation and older distribution maps can be unreliable .). An effort is currently underway to generate new distribution maps of all periodical cicada broods . This effort makes use of crowdsourced records and records collected by entomologists . </P> <P> Not only are the periodical cicada lifecycles curious for their prime numbers 13 or 17, but also their evolution is intricately tied to one - and four - year changes in their lifecycles . One - year changes are less common than four - year changes and are probably tied to variation in local climatic conditions . Four - year early and late emergences are common and involve a much larger proportion of the population than one - year changes . </P>

Where are cicadas found in the united states
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