All Magicicada species have a black dorsal thorax with red eyes and orange wing veins. Cassini periodical cicadas are smaller than decim periodical cicadas. The abdomen is black except for occasional faint orange-yellow marks on the ventral surface seen in some location. In a typical brood of periodical cicadas, decim and decula types will be present as well as cassini.
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The same study estimates that the Decim species group split from the common ancestor of the Decula plus Cassini species groups around 4 million years ago (Mya). At around 2.5 Mya, the Cassini and Decula groups split from each other. The Sota et al. (2013) paper also calculates that the first separation of extant 13-year cicadas from 17-year cicadas took place in the Decim group about 530,000 years ago when the southern M. tredecim split from the northern M. septendecim.
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In each species group, Decim, Cassini, and Decula, the signature of the glacial periods is manifested today in three phylogeographic genetic subdivisions: one subgroup east of the Appalachians, one midwestern, and one on the far western edge of their range. The Sota et al. data suggest that the founders of the southern 13-year cicada populations seen today originated from the Decim group. These were later joined by Cassini originating from the western Cassini clade and Decula originating from eastern, middle, and western Decula clades.
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Anon: "Registry of the Monastery of St Augustine", Cart 325, Decim Script col 1921. Canterbury. Lora de Ros, lady of Horton, gave her right to two carucates of land and of woods in Plumstead to the abbot, Thomas, in return for the rights of her and her heirs to partake of prayers performed in the church during 1287.Anon: "Registry of the Monastery of St Augustine", Cart 311 & 370, Decim Script col 1942, 1949. Canterbury. It appears that Robert, the last abbot but one, had recovered a share of this land from her ancestor, Richard de Ros.
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Mature females are slightly larger than males. Magicicada males typically form large aggregations that sing in chorus to attract receptive females. Different species have different characteristic calling songs. The call of decim periodical cicadas is said to resemble someone calling "weeeee-whoa" or "Pharaoh".
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The second noteworthy event took place about 320,000 years ago with the split of the western Cassini group from its conspecifics to the east. The Decim and the Decula clades experienced similar western splits, but these are estimated to have taken place 270,000 and 230,000 years ago, respectively. The 13- and 17-year splits in Cassini and Decula took place after these events. The 17-year cicadas largely occupy formerly glaciated territory, and as a result their phylogeographic relationships reflect the effects of repeated contraction into glacial refugia (small islands of suitable habitat) and subsequent re-expansion during multiple interglacial periods.
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The three different types have unique species song-types; they also tend to sing at different times of day, with cassini choruses most likely in mid- to late afternoon, later than decim or decula varieties. The cassini-type song consists of a series of ticks followed by a buzz; it has also been described as sounding like "someone trying to get a lawnmower started." Magicicada males seek out sunlit vegetation, where they typically gather with conspecific males to form large choruses, alternating singing behavior with short flights. Cassini-type males are unusual in synchronizing these behaviors, so that thousands of males sing their mating song in unison and then fly together.
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King Edward the Confessor restored them again to the monastery on taking power, however Tostig saw the opportunity to take possession of them once again after Edward's death in 1066 when King Harold seized his brother's estates. After the Battle of Hastings in 1066, William the Conqueror gifted Plumstead to his half-brother Odo, Bishop of Bayeux whom he also titled Earl of Kent. The Archbishop of Canterbury Lanfranc of Pavia and the Norman abbot of St Austin's successfully interceded to reclaim a portion of the land on behalf of the monastery. In 1074 Odo then granted by deed the remainder of the parish and also the right of the abbot to be "Chief Lord of the Fee".Anon: "Registry of the Monastery of St Augustine", Cart 163 & 200, Decim Script col 1779, 1787. Canterbury.
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