There are seven species of periodical cicadas. These are most easily distinguished by the very specific male call. Each species has as its closest relative a species with the alternate lifecycle. While it may be that in fact these are not actually seven distinct species, they are considered as such until more data comes in to resolve this question.

13-year cicada species:
• Magicicada tredecim (Walsh and Riley 1868)
• Magicicada neotredecim (Marshall and Cooley 2000)
• Magicicada tredecassini (Alexander and Moore 1962)
• Magicicada tredecula (Alexander and Moore 1962)
17-year cicada species:
• Magicicada septendecim (L. 1758)
• Magicicada cassini (Fisher 1851)
• Magicicada septendecula (Alexander and Moore 1962)

Magicicada tredecim has a 13-year cycle. It is similar morphologically to M. septendecim and to M. neotredecim; these three species are frequently referred to as the “decim group”. Its coloring is lighter than other periodical cicadas, often a light orange color on the ventral abdomen. The call of M. tredecim is very similar to M. septendecim. In 1998 M. tredecim was found to be two species, distinguished by call frequency and mitochondrial DNA. The other species was named M. neotredecim.

(Cooley, 2011; Cooley and Marshall 2011; Hill and Marshall 2011; Marshall and Cooley 2000; Simon 2011; Wikipedia 2011)