The cicadas are in the forecast – What you need to know about Brood X – Six Mile Post
Brood X, aka Great Eastern Brood, is a large group of periodic cicadas or “magicicadas” that emerge every 17 years in 11 states, including Georgia. Brood X is made up of three different species: Magicicada septendecim, Magicicada Cassini, and Magicicada septendecula.
Jason Christian, biology instructor at GHC, remembers Brood X’s last appearance in 2004. “I’ve always been an avid outdoorsman, so the high density of them in nature is always a memorable experience though. you have to find yourself outside when they’re outside, ”Christian said. Christian has studied ecology for over 10 years and during his 8 years at GHC he has helped many of his students collect and identify cicadas for insect projects.
Brood X’s periodic cicadas are not the same as the annual cicadas that set the mood Georgia summer evenings every year. While annual cicadas have populations that emerge each year, periodic cicadas emerge in cycles of 13 or 17 years.
The most striking visual difference between these cicadas is their color palettes – annual Georgia cicadas tend to be shades of green, while periodic cicadas are black with red eyes. Periodic cicadas are also smaller and have distinctly different songs than their annual cousins.
Northern Georgia counties such as Gilmer, Union and White are likely to see the insects appear this summer.
“The densities [Brood X] can emerge in their strongest concentration [and] can reach 1.5 million per acre! Christian said, “North Georgia is in the lower part of their range which spans most of the eastern United States. Not everyone will see or hear the greatest of emergencies because they are not distributed evenly across northern Georgia. So, some will encounter high densities and others will not even notice anything happening.
“The emergence is triggered when soil temperatures at 8 inches deep reach around 63 to 64 degrees, so in northwest Georgia it could be as early as late April or up to mid-May.” , said Christian.
When the weather warms up, thousands of cicadas will dig their way out of the ground and climb the nearest vertical surface to molt, leaving behind their molted exuvia or exoskeletons. Once the wings of adult insects have stiffened or hardened, they lift off to find a mate.
Once they emerge, cicadas only live for a few weeks, but during that time they accomplish a lot. “Males use special organs in their abdomen to vibrate the air in order to ‘sing’ their mating cry,” Christian said.
“Most people know the song of the cicadas,” Christian said, “even if they don’t know it’s the sound you hear. To me it is the sound of summer, when you are in nature during the day you hear various “buzzes” coming from the area around you, what most often makes these noises are the cicadas! Cicadas are known to be quite loud. Some species have been recorded producing over 100 decibels of noise in their mating calls – roughly the equivalent of a chainsaw or a motorcycle.
“When a woman finds singing to her liking, she will mate. It lays its eggs on a tree, then the adults die, ”said Christian.
A few weeks later, their offspring hatch and head for the ground to start the 17-year cycle again. Cicada nymphs spend most of their lives burrowing underground and feeding on plant roots.
But why do they spend so long underground? Christian explained that cicadas do this to avoid predators. “Not all species spend as much time underground,” Christian said, “but the lag of years prevents too many species from synchronizing with their predators. If everyone went out at the same time, then over time the predators would react the same and that would be a negative pressure on the survival of the cicadas.
“Cicadas are a big part of the food chain. It’s basically Thanksgiving dinner for almost all predators during these major emergencies, ”Christian said. Birds, fish, rodents and other insects are among the many predators cicadas.
After 2021, Brood X will not be seen again until 2038. Georgia will see a few more broods before then, including the next emergence of Brood XIX in 2024 – which will be an even bigger event in Georgia than this summer. Even though cicadas pose no danger to humans or pets, people with entomophobia may be tempted to stay indoors or travel out of state as 2024 approaches!
Those of us who aren’t averse to creepy critters can lend a hand in a scientific cause by helping to map the emergence of Brood X.
Anyone who sees or hears a cicada can record their sightings with the University of Connecticut. Cicada tracker or with the Cicada Safari application developed by Mount St. Joseph University. Scientists at the University of Connecticut are interested in tracking the 2021 emergencies in northern Georgia, in particular, as some of the cicadas here could be stragglers of Brood VI.