Decim periodical cicadas is a term used to group three closely related species of periodical cicadas: Magicicada septendecim

Magicicada septendecim

Magicicada septendecim, sometimes called the Pharaoh cicada, is a species of periodical cicada with a 17-year life cycle, native to Canada and the United States...

, Magicicada tredecim

Magicicada tredecim

Magicicada tredecim is a 13-year species of periodical cicada, closely related to the newly discovered 13-year species Magicicada neotredecim, from which it differs in its in male song pitch, female song pitch preferences, abdomen color, and mitochondrial DNA. Both M. tredecim and M. neotredecim...

, and Magicicada neotredecim

Magicicada neotredecim

Magicicada neotredecim is the most recently discovered species of periodical cicada. Like all Magicicada species, M. neotredicim has reddish eyes and wing veins and a black dorsal thorax. It has a 13-year life cycle but seems to be most closely related to the 17-year species Magicicada septendecim...

. M. septendecim, first described by Linnaeus, has a 17-year lifecycle; the name "septendecim" is Latin for 17. M. tredecim, first described in 1868, has a similar call and appearance but a 13-year lifecycle; "tredecim" is Latin for 13. M. neotredecim, first described in 1962, is a 13-year species but otherwise much more similar to M. septendecim than to M. tredecim.

Description

Like other species included in Magicicada

Magicicada

Magicicada is the genus of the 13- and 17-year periodical cicadas of eastern North America. They are sometimes called "17-year locusts", although cicadas belong to order Hemiptera, while locusts are Orthoptera....

, decim periodical cicadas have synchronized development with a long larval period underground (13 or 17 years, depending on species), followed by mass emergence, quick development to adult flying forms, and massed singing choruses of males that attract many females. Mating, egg-laying, and the death of all adult cicadas occur within weeks. Eggs hatch into first-instar larvae, which tunnel into the earth to begin their own multi-year subterranean feeding period.

All Magicicada species have a black dorsal thorax and orange wing veins. Their large compound eyes, and the three ocelli arranged in a triangle between two eyes, are red. All three decim species show orange coloration on the underside of the abdomen: broad orange stripes in the case of M. septendecim and M. neotredecim, solid orangish or caramel color in the case of M.tredecim.

Magicicada males typically form large aggregations that sing in chorus to attract receptive females. The decim periodical cicadas share a distinctive song said to resemble someone calling "weeeee-whoa" or "Pharaoh". The Encyclopedia of Entomology describes a decim song pattern as "pure tone, musical buzz ending in a drop in pitch".

The calling song of M. tredecim has a slightly lower pitch than those of M. septendecim and M. neotredecim. M. neotredecim was first identified when scientists noticed a bimodal split in the dominant pitch (frequency) of male calling songs during the 1998 emergence of Brood XIX

Brood XIX

Brood XIX is the largest brood of 13-year periodical cicadas, last seen in 1998 and reappearing in May and June of 2011 across a wide stretch of the southeastern United States...

.

The dominant song pitch of M. neotredecim ranges from 1.25 to 1.90 kHz. (This is similar to the pitch-range of M. septendecim except that songs of the 17-year species do not extend so far into high frequencies.) M. neotredecim song frequencies have been obseved to displace upward in areas where their range overlaps with the similar M. tredecim, whose dominant song pitch is lower, ranging between 1.00 and 1.25 kHz.

These distinctive calling songs prompted a closer look at older data concerning M. tredecim. Two different forms of mitochondrial DNA, correlated with a difference in abdominal color, had already been seen in insects assigned to this species. David Marshall and John Cooley determined that these known differences correlated with the observed pitch difference in males and a corresponding pitch preference in females. The name M. neotredecim was given to the variant whose song, abdominal coloring (orange with a black lateral band or center), and mitochondrial DNA resemble the 17-year species M. septendecim. The earlier name M. tredecim was reserved for the group whose abdomen is mostly orange, whose song has a lower pitch, and whose mitochondrial DNA differs slightly from the two other species of decim cicadas. The mitochondrial DNA difference observed suggests that the M. tredecim lineage separated from the other decim line about one million years ago.

Habitat

The decim cicadas live in (roughly) the southeastern quadrant of the United States. They are typically found in upland woods and forest-prairie ecotones, favoring deciduous trees and shrubs both for chorus locations and for laying their eggs. Nymphs can survive feeding on the roots of many different kinds of plants, including conifers as well as deciduous trees.