Brooding Cicada

Here's another one of the periodical cicadas I met at Sourland last week. Today I want to give a fairly quick discussion not of brooding cicadas with emotional issues, but of the cicada broods themselves.

Our periodical cicadas consist of 3 groups, 7 species and 15 broods. The 3 groups consist of extremely similar species, sometimes where the main difference between the species is the brood cycle. Note I can't use common names since some of these guys don't have a common name beyond the periodical cicada umbrella. Here are the groups:
  • Decim group. This is the biggest group, with 3 species. It has 1 17-year cicada species, Magicicada septendium (Pharaoh Cicada), and 2 13-year cicada species, Magicicada tredecim and Magicicada neotredecim. DNA differences and slight differences in their calls has led entomologists to split M. neotredecim off from M. tredecim. Just looking at them, you probably wouldn't be able to distinguish any of these cicadas.
  • Cassini group. This group has 2 species, the 17-year cicada Magicicada cassinii (Dwarf Cicada) and the 13-year cicada Magicicada tredecassini. Once again, these two species are virtually impossible to tell apart from one another. A Maryland naturalist claimed the main difference between the cicadas in this group and the other groups is that they have all-black abdomens.
  • Decula group. Another 2-species group, this one consists of the 17-year cicada Magicicada septendecula and the 13-year cicada Magicicada treducula.
The takeaway from that is that each of the 17-year cicada species has as its closest relative 1 or 2 13-year cicada species. Apparently these 3 groups each developed their own 17-year species and 13-year species.

Most broods, both 17-year and 13-year, contain each of the species associated with their cycle. For example, this year's Brood X consists of each of the 17-year species: Magicicada septendium, Magicicada cassinii, and Magicicada septendecula. I don't think every Brood X area has all 3 species (most of the ones I got pictures of have been IDed as Magicicada septendium, and none have been identified as another species), but at least across the continent Brood X is represented by all 3 17-year cicada species. So if some of your periodical cicadas look/sound different from others, they might just be separate species.

The 13-year broods are located in the South or the Midwest. The 17-year broods don't appear as far south, but make up for that with more northern broods.

Although lots of cicadas show up on schedule for their brood, it's not an exact science on the part of the cicadas. Some individuals will show up off schedule, usually by 1 or 4 years; 2017 was a Brood X straggler year.
May 27, 2021 at Sourland Mountain Preserve
Photo 133213097, (c) jpviolette, some rights reserved (CC BY-NC)


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