This year already was a rare one in Central Illinois because of a solar eclipse. The next happening is even rarer — two broods of cicadas, one on a 13-year cycle, the other on a 17-year cycle, will emerge from the ground this year at the same time.
It's the first time that has happened in a couple hundred years and could make for an exceptionally noisy spring and early summer.
Illinois State University biologist Scott Sakaluk is a behavioral ecologist who has done work in entomology among other areas. He said Central Illinois is a great place to be to get the best of both broods.
“I think they're going to overlap perfectly. It's a small version of cicada-geddon,” said Sakaluk.
They will make music, mate, and die over a period of weeks.
Trillions and trillions
Some scholars have measured cicada populations as high as one 1.5 million per square acre. That works out to about 800 tons of bug per square mile.
Sakaluk said he’s curious to find out what effect the mass hatch will have on animals. He works with bird populations in the Merwin Nature Preserve at the Parklands Foundation. In recent years, there have been problems with hungry raccoons climbing into nest boxes and grabbing young birds.
“I'm really curious to see whether or not this super abundance of cicadas is going to have an effect on the levels of predation of our birds. I'm hoping it has a really salutary effect,” said Sakaluk. “Raccoons have very cosmopolitan diets and they're not going to pass up a super abundance.”
Raccoons aren’t the only animals that could benefit. He said birds such as bluejays and starlings, and a variety of mammals and reptiles gorge on cicadas.
“These pulses of protein the cicada emergences represent, can have a really marked effect on at least some of the birds and mammals,” said Sakaluk.
Depending on the species, the population boost given by having more young animals survive to adulthood can last several years before returning to a baseline, he said.
The effect on plants might be more mixed.
The larvae feed on the sap of roots, called xylem, with piercing and sucking mouth parts. So do adults. More important, Sakaluk said, is what happens when females lay eggs that can damage trees.
“When females have mated and they're ready to lay their eggs, they make v-like incisions in young twigs. They might lay 120 eggs or so. You've got so many of these females out there doing that, that can really do damage to a lot of trees,” said Sakaluk. “People who manage orchards, for example, in years where there's going to be an emergence, don't plant new young trees, because they know that they're going to die. It can cause some economic damage.”
“On the plus side, when all those cicadas die, they represent a massive fertilization boost. You've got this enormous nitrogen source.”
Come on feel the noize
When the two periodic broods add their mating song to the regular chorus of annual cicadas, people may notice a louder sound this year.
“And they're loud insects. Even on an individual level, they're really impressive,” said Sakaluk.
Only the males buzz. They are loud because of the way they're built. And it’s not the wings that make the sound. In their abdomens, Sakaluk said, they have two rigid discs that are made of chitin. Those are called "tymbals."
“As a metaphor, the little metal insects you used to get in the dime store, where you push on them, you click on them, and they click back and make a sound? That's exactly how a tymbal works,” said Sakaluk.
They do this rapidly and alternate sides. Another analogy that helps explain the volume is that a male cicada body is similar in design to a speaker.
“Most of the interior of the abdomen of a male is hollow. There's nothing else there other than a narrow intestinal tract. That empty abdomen acts as a resonance chamber and it really amplifies that signal,” said Sakaluk.
Abba vs Queen
Each brood of cicadas is not a single species, there are several. And each species has its preferences much as people differ on the virtues of "Dancing Queen" and "We are the Champions." The songs vary from species to species, usually by time, Sakaluk said, so there is little chance of interbreeding of the broods that are emerging together.
“The females of the respective species of the males recognize the stereotypical signal that's being produced by the male, and they will respond only to that signal,” said Sakaluk.
There is math too
This is the first time the two broods have emerged at the same time since 1803.
“One of them is on a 17-year cycle. The other one is on a 13-year cycle — 13 and 17 are prime numbers. That means they're only going to coincide in time every 13 x 17 years, which is 221 years. The last time that happened in McLean County, would be that long ago,” said Sakaluk.
Some experts say cicadas start to emerge from the ground, molt, and assume their adult form when the soil temperature rises to about 65 degrees. Sakaluk speculated there could be a photo sensitive mechanism that contributes to the emergence trigger as well.
He said the best places to hear cicadas are anywhere where there are trees or pockets of forest.
“Certainly, we're going to get lots in town because there are lots of trees in town,” said Sakaluk.
The Parklands Foundation along the Mackinaw River north of Bloomington-Normal also will be a likely place to hear the full song of the cicada this year.
