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 septendecim is a 17-year cicada, and the largest and most familiar of the all the periodic cicadas. It is morphologically and behaviorally similar to M. tredecim and M. neotredecim; these three species are classed together as the closely related “decim” group, and share a similar call, which sounds like “Pharaoh”.

(Cooley, 2011; Cooley and Marshall 2011; Wikipedia 2011)