Decim Difficulties

More and more adult Magicicada are emerging in the northern part of Brood XIX's distribution, and along with them comes the difficulty of identifying the two decim species in the brood: M. tredecim and M. neotredecim. While it's true that M. neotredecim is more closely related to septendecim and tends to be darker, variation is present in all three decim species. I've seen septendecim in previous emergences that were nearly devoid of black on the underside of the abdomen, and I've also seen surprisingly dark tredecim (in areas where only tredecim is present).

M. neotredecim is no exception; it also varies and can be a bit lighter or darker than is typical. John Cooley, who along with Dave Marshall originally described the species, noted that a population in central Illinois is atypically light: see his description of the 3D model here: https://cicadas.uconn.edu/m_neotredecim/

This is why I'm doubtful that coloration alone is a good enough feature for species ID, and why I'll continue to stick with complex-level (more accurately, species group) IDs in areas where both species are possible. As a rule of thumb, reliable genus-level records are more valuable than questionable species-level ones.

Sound recordings, on the other hand, have the potential to be very useful; high-pitched, "displaced" calls occur in areas where neotredecim and tredecim overlap. (See https://cicadas.uconn.edu/rcd/) It would be great to build a good collection of these on iNaturalist!

Publicado el mayo 13, 2024 08:05 TARDE por weecorbie