How exactly do billions of cicadas know to emerge out of the ground at almost the exact same time?
The historic synchronization is already beginning as two broods that events emerged together in more than 220 years simultaneously come out of the ground.
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WATCH HEREExperts say the process is known as synchronization, which has been studied for centuries.
“The study of synchronization is itself rooted in physics, often considered to have originated with Dutch physicist Christiaan Huygens’ studies of pendulum clocks in the 17th century. Synchronization is now recognized as an important behavior across many domains — from engineered systems like power grids, to biological systems such as neuron firing in the brain, to other ecological phenomena such as the coordinated production of fruit by oak trees," Northwestern University’s Jorin Graham, a Ph.D. student in physics studying network science. "Remarkably, such synchronized behavior is commonly achieved without centralized planning or enforcement."
So how does it work with cicadas?
According to Graham, each cicada counts the years underground using "annual cycles of xylem flows, a nutritious fluid in trees on which they feed."
Depending on which periodical cicada they belong to, 13- or 17-year cicadas will then wait to emerge with the rest of their brood in the same year.
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But it doesn't always work.
Graham said some cicadas, considered "stragglers," miscount the year and emerge either earlier or later than the rest of their broods. If those cicadas reproduce, their offspring then become out of synchronization.
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"Synchronization is preserved by predators, such as squirrels, who quickly consume cicadas that emerge at the wrong time," Graham said. "During normal emergence years, so many cicadas come out that predators can’t eat all of them, allowing the remaining cicadas to reproduce, thus sowing the seed for the next coordinated emergence.”
That's certainly the case with the the historic 2024 emergence, which will bring billions of cicadas to the surface.
The two emerging broods are Brood XIII and Brood XIX, which haven't emerged together in 221 years.
"This is like the year for Illinois," cicada expert Catherine Dana, an affiliate with the Illinois Natural History Survey, told NBC Chicago. "We are going to have cicadas emerging all over the state."
While signs of the emergence have been spotted for weeks, the true peak in the Chicago area is expected any day.
"The periodical cicadas will start emerging when the soil temperature eight inches below the ground gets to 64 degrees," Jennifer Rydzewski, an ecologist with the Forest Preserve District of DuPage County, told NBC Chicago.
That is likely with a warm weekend in store for much of the area.
"It's getting really close," Rydzewski said.
The emergence has started earlier than average in Illinois, but much of the region has yet to see the swarms of cicadas being warned about and the defeaning sounds that have sparked 911 calls in some states.
According to some experts, the emergence of the first cicadas came about two weeks ahead of the historic average. It will continue to be sporadic, however, as soil temperature, mulch and turf grass all impact cicadas differently. For example, the soil is warmer near pavement, so cicadas in the those spots are expected to emerge quicker.
When cicada nymphs first come out from the ground, they climb up to a tree or another high place and shed their shells.
In a year of full emergence, after the bugs surface, they then begin mating, which is often met with the noise most associate with cicadas. Experts with the DuPage Forest Preserves said it takes about a week from emergence before cicadas begin mating.
Cicadas have a lifespan of approximately four weeks, meaning the emergence is set to last through at least mid-June.
Where the emergence will be seen
For the Chicago area, Brood XIII will be most seen in parts of northern Illinois and Indiana, and possibly even in Wisconsin and Ohio.
The Northern Illinois Brood itself is huge, with a reputation for the "largest emergence of cicadas anywhere," according to the University of Illinois.
Meanwhile, Brood XIX, or the Great Southern Brood cicadas, have a more widespread population, covering parts of Missouri, Illinois, Louisiana, North Carolina, Virginia and Maryland.
"Brood XIX is arguably the largest (by geographic extent) of all periodical cicada broods, with records along the east coast from Maryland to Georgia and in the Midwest from Iowa to Oklahoma," the University of Connecticut reports. "Although 13-year cicadas are generally considered to have a southern distribution, the northernmost known record of this brood is in Chebanse, IL, roughly 75 miles from Chicago’s Loop."
Across most of Illinois and the Chicago area at least one of the two broods is likely to emerge, but in a narrow part of the state, both could emerge at the same time, in the same place.
"Somewhere around Central Illinois, probably like around Springfield, is what some researchers are predicting we may see some overlap of these two ... different broods," Dana said. "It's not going to be a large area. But there will likely actually be some mating happening between these two broods, which is going to be really exciting."
Here's a map of what to expect in Illinois, according to data from the USDA Forest Service.
