Photo by Katja Schulz. CC BY 2.0 DEED, creativecommons.org/licenses/by/2.0.
Cicada
This summer, millions of Americans will get a glimpse at the mysteries beneath the earth’s surface. And that glimpse will be loud.
In a historic overlap of entomological timelines, two broods of periodical cicadas will emerge after over a decade underground—where they have lived most of their lives as nymphs, feeding on sap and tree roots—to mate, sing, lay eggs, and die. Known as Northern Illinois Brood (Brood XIII) and the Great Southern Brood (Brood XIX), the cicadas’ generations cycle through every seventeen and thirteen years, respectively. The last time these two broods emerged simultaneously was 1803.
The Great Southern Brood, which last emerged in 2011, is one of the largest of all periodical cicada broods (as opposed to annual cicadas, which have shorter lifespans, that emerge each year) and occupies a territory ranging from Maryland to Georgia and from Iowa to Oklahoma. The Northern Illinois Brood, which last emerged in 2003, is much smaller—its geographical range limited to areas in Michigan, Indiana, and Ohio.
“If chorusing and reproduction are observed, that makes them part of Brood XIX by default." —Dr. Christopher Carlton
Historically, the Great Southern Brood’s range has extended somewhat into northeast Louisiana—though this is up for some debate. “The documented records from the northern part of the state are very old—they go back hundreds of years,” explained Dr. Christopher Carlton, an Entomology Diagnostician at the LSU AgCenter and professor at LSU. “And if you look at different maps [of the Great Southern Brood’s distribution], you’ll see some localities in Louisiana, and other maps won’t show any. We’re not really sure of the actual distribution of this brood from the very beginning.”
When the brood last emerged in 2011, no cicadas were sighted here. According to Carlton, this suggests that if there was an active Louisiana population of the Great Southern Brood, it may have gone extinct. He explained that during the cicadas’ growth period, they must have access to viable tree roots. And being relatively immobile, they rely on the place they feed to remain stable for the entire thirteen years they are underground. “So anything that destroys that area during that thirteen year period—which is a long time—if you clear cut the trees and build a parking lot, then you eliminated their food source,” and thus, the entire population in that area.
Hope is not entirely extinguished, though. As of mid-May, Carlton said he had noted about half a dozen verifiable records of cicada sightings reported on iNaturalist in North Louisiana. “The problem with a lot of these observations is that there are no comments on them,” he said. “So you don’t know if this is a single cicada, or if there is a chorusing and reproduction event going on.”
There is still time for more cicadas to crawl up through the northeast Louisiana soils. All citizen-scientist sightings can be reported through iNaturalist or the Cicada Safari App. Cicadas coming from the Great Southern Brood, as opposed to other periodical broods or annual cicadas, will be the only ones singing this summer. “If chorusing and reproduction are observed, that makes them part of Brood XIX by default,” said Carlton.
