2021 will see the noisy emergence of Brood X cicadas after 17 years underground. So, what’s special about Brood X, and why do cicadas do what they do? Clyde Sorenson, Alumni Association Distinguished Undergraduate Professor of Entomology at NC State, sheds some light on the life and times of the cicada.
According to Sorenson, a cicada starts out as an egg, usually laid in a slit in a twig, on a plant, which then drops to the ground and tunnels down into the earth. The nymph then finds a tree root and it starts feeding on liquid from those roots. It goes through several nymphal stages before it eventually gets big enough to come up to the surface, molt one last time into the adult stage, find a mate and repeat the cycle.
When we look at cicadas, they fall into two major groups in Eastern North America: what we call the dog-day cicada, or annual cicadas, some of which come up every year; and the periodical cicadas which, in a particular geographic location, only show up every 13 or 17 years.
“They have to have long life cycles because it takes them several years to grow up feeding on the tissue that they feed on,” Sorenson says.
The two types of cicadas have different strategies when it comes to survival: annual cicadas tend to be wary and avoid predators, whereas periodic cicadas essentially overwhelm predators with their numbers.
“If we all come out together every 13 years or every 17 years, if we all come out at the same time, there are simply too many of us for the predators to eat all of us,” Sorenson explains. “We call that theory the predator satiation theory.”
The most recognizable thing about cicadas is their song. Only males sing, and they do it through special structures on their abdomens called tymbals – plates of ridged cuticle attached by a strut to a huge muscle that contracts extremely rapidly. Surrounding the tymbal are air cells that act as drum head amplifiers.
“When you deflect the plate, it snaps and it creates a little tiny sonic boom,” Sorenson says. “And when you release the plate, it snaps again and it makes another sound. And so cicadas make their sounds by deflecting these plates of cuticle at insanely high rates of speed.”
Cicadas are the loudest insects in the world and amongst some of the loudest animals in the world, at least some species. Some species have calls that exceed a hundred decibels, so it’s like standing beside a jet engine.
This year’s emergence is called Brood X, a brood of 17-year cicadas and one of the largest broods in terms of geographic extent.
But in North Carolina if you want to see Brood X, you’re going to have to go to the northwestern and southwestern parts of the state.
According to Sorenson, North Carolina’s big cicada brood will emerge in 3 more years.
“Our big brood in this part of North Carolina is Brood XIX of the 13 -year cicadas, and that’s going to happen in 2024,” Sorenson says. “North Carolina has pieces of six different broods, but because two of those broods that we have pieces of are 13-year cicadas, over a 17-year period, we have cicadas every seven or eight years.”
Did you know that you can recognize different cicadas by their songs? If you love hearing cicadas sing, Sorenson recommends visiting Songs of Insects. Their cicada page features a variety of songs from different cicada species.