2024 Double Brood Periodical Cicada Event: What to Know

by Dalen Gardeneer
March 07, 2024
1 min read

Detailed macro image of the cicadas in the branches of small tree

13-Year and 17-Year Cicadas Converge in 2024

Two Broods, including seven species, emerge all together for the first time in 221 years. Scientists expect a symphony of different-sounding cicada songs in a rare, grandiose mating ritual.

Found on every continent except Antarctica, cicadas are regularly maligned, often associated with Biblical locust plagues, widespread destruction, and simply cases of creepy crawlies. Some find the cicada song a delightful harbinger of summer days, but others find them a nuisance, especially during years of large emergences.

While we can expect to see a brood of cicadas every spring and summer, some years bring larger emergences — like the simultaneous breakout of two distinct periodical broods in 2024. Brood XIII and Brood XIX last had a chance to see each other in 1808, and they won’t have another opportunity to cross paths (and cross-breed) for another 221 years.

When Are the Cicadas Coming Back?

Don’t be fooled into thinking it’ll be another 17 years before you see another cicada. As a rule of thumb, you can expect different periodical broods to emerge just about every year. So, while you won’t see Brood XIII for another 17 years, Broods XIV, XXII, XXIII, etc., will emerge one year after another. Some of these are 13-year cicadas, and others are 17-year cicadas. Every year is an emergence year for a different cicada brood that has been waiting.

How Often Do Cicadas Come Out?

Besides periodical cicadas, there are also annual cicada emergences. The annual cicadas tend to look more green, while the periodical cicadas look more brown and orange. Annual cicadas have a much shorter life cycle: one year under the soil and then back up to mate, reproduce, and die. The larvae crawl back under for a year and come back out again the following year. In other words, an annual cicada is a 1-year cicada, which puts into perspective how marvelous the periodical cicadas are. 13-year cicadas are very old compared to annual cicadas. And it makes the 17-year cicadas seem relatively ancient!

Where Do Periodical Cicadas Come From and Where Will They Go?

During the years of periodical cicada emergences, millions of cicada nymphs that have been living beneath the soil emerge from the ground, climb trees, shed their exoskeletons, and serenade each other from the trees. As a fully fledged adult, the cicadas barely eat — so don’t worry about your garden produce getting gnawed by the emergence — but spend their brief time aboveground loudly searching for a mate, breeding, and laying eggs.

This large chirping insect that we’re familiar with is actually the final of five forms (technically known as instars) that make up the full life cycle of a cicada. The first is a small, rice-shaped, nearly translucent egg. The second is a first instar nymph. It’s small and delicate, appearing almost made of jelly, and looks nothing like its adult form. The following stages are second, third, and fourth instar nymphs, with each stage of development appearing closer to its final stage, known as the imago.

While in their nymph form, cicadas feed by sucking the sap from tree roots. Though this sounds alarming, there is evidence that, far from harming the trees, this behavior is quasi-symbiotic and can benefit them instead.

Cicada Broods Reunited After 221 Years, Won’t Happen for Another 221

In 2024, both Brood XIII and Brood XIX will emerge when soil temperatures reach around 64 or 65 degrees Fahrenheit. This has not happened since 1803, and it will be another 221 years before these two broods can meet again. In the meantime, they will continue to periodically emerge every 13 and 17 years for Brood XIX and Brood XIII, respectively, until they sync up again in the year 2245. This year’s 2024 double-emergence is a rare opportunity for these two distinct cicada broods to mate and cross-breed, potentially forming new species and new broods.

Cicada Broods Reunited After 221 Years, Won’t Happen for Another 221

Great Eastern Periodical Cicada perched on a pink azalea

Brood XIII and Brood XIX are different because they emerge at different rates. Brood XIX emerges every 13 years, and Brood XIII emerges every 17 years.

While researchers are still exploring how the cicadas can time their emergence and appear all at once, there is the preliminary hypothesis that they have an internal molecular clock, adjusted each year by signals such as changes in the sap they eat. After their internal clock has “counted off” the determined number of years, their emergence occurs when ground temperatures warm to a certain level, usually around 65 degrees.

Understanding how one brood differs from another is complicated because each brood has a subset of species. There are four different species within Brood XIX. There are three different species within Brood XIII. That's seven different species between the two cicada broods.

The differences between the species are usually subtle. One might have thicker orange stripes on its abdomen, while another might have thicker black stripes. One species is a smaller dwarf, while another is much larger.

Putting aside the differences, all species within Brood XIII emerge every 17 years. All species within Brood XIX emerge every 13 years. And there is a whole lot of variety amongst all the species of both broods!

Where Will the Cicadas Emerge in the United States?

The cicada emergence this year could span as many as 18 states, but there is one state in particular where the two periodical cicada broods are expected to overlap: Illinois.

Based on historical sightings, the Brood XIX species are expected to emerge in states like:

Alabama
Arkansas
Georgia
Illinois
Indiana
Iowa
Kentucky
Louisiana
Maryland

Mississippi

Missouri

North Carolina

Oklahoma

South Carolina

Tennessee

Virginia

Washington, D.C.

Brood XIX will likely emerge first due to warmer temperatures in the south.

Brood XIII is expected to emerge only in: Based on historical sightings, the Brood XIX species are expected to emerge in states like:

Illinois
Indiana
Iowa

Michigan (possibly)

Wisconsin

This cicada year, Springfield, Illinois, will be the real hot spot for the overlap of the two broods, where the two broods might have a chance of cross-breeding.

Map of areas where cicada emerges will occur

Will Cicadas Eat My Garden and Damage My Trees?

The only real risk of damage from cicadas is “flagging,” which occurs when the females deposit eggs in small grooves they make in branches. If enough females choose the same branch, the branch can turn brown and even die. For adult, healthy trees, the cicadas can actually act like “pruners” because they choose the weakest branches of the trees to lay their eggs.

Dan Mozgai, of the highly informative website devoted to cicadas, Cicadamania.com, says, “The weakest limbs of a tree are often temporarily damaged or killed off, the result of which is called flagging, as the leaves of the branch will turn brown and look like a hanging flag. In many cases, they are doing the trees a favor by pruning their weakest branches.”

But for saplings, recently planted trees, very delicate trees, or unhealthy ones, a cicada brood emergence can kill them off. Some experts suggest holding off from planting new trees until after an emergence has passed. Those with young and tender trees should protect them for peace of mind — products like the Pop Net and Harvest Guard can help provide this kind of protection.

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Fortunately, products like Dalen’s Pop-Net Protective Pest Screencan help keep cicada nymphs from feeding on your prized plants.

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Will the 2024 Cicada Year Be Louder Than Normal?

This year, the cicadas could be louder, depending on your location. Cicadas are one of the loudest insects known to man, with their chirping or “song” as loud as 100 decibels. The organs males possess that make the distinctive call are called tymbals. The tymbal is a membrane the insect can flex back and forth using strong muscles, creating a clicking sound. Groups of cicadas are sometimes described as sounding like some sort of alien UFO.

Each cicada species has a distinct mating call, which can also change how loud they are in your area. Brood XIII will sound different than Brood XIX, but the different species within each cicada brood will also sound different!

For example, Cicada Neotridicum, a species belonging to Brood 19, will alter its song to a higher pitch to differentiate itself from other species within Brood 19. Female Cicada Neotridicums generally will recognize and prefer the higher pitch mating call of the species to which they belong.

Although they all may look similar, all species should sound different. Brood XIII males will sound different from Brood XIX males. All four species within Brood 19 will sound different, as will all three species within Brood 13. That means there should be at least seven different-sounding cicada species emerging in 2024! But who knows how the cicadas will alter their tunes when confronting another species! The subtle differences could be extraordinary!

In most places, you’ll only hear one species. But scientists expect a symphony of cicada songs in the overlapping hotspots like Springfield, Illinois, where multiple species belonging to both broods emerge.

Scientists are excited to see how the females react. Will Brood XIII females fancy a Brood XIX male? While cicadas prefer familiarity, some might be enticed by a novel mating call. And there might be some confusion. In any case, an entirely new cicada could be the offspring and outcome.

But what would happen if a 13-year cicada mates with a 17-year cicada? Would the new cicada brood split the difference and become a 15-year cicada? Which species of which brood is the mother? Which species of which brood is the father? How long will these new cicadas live? Questions like these are why cicada scientists and enthusiasts are flocking to Springfield, Illinois, this summer.

Will More Cicadas Mean More Cicada Shells?

Another reason homeowners tend to dislike cicadas is their molting. Cicadas, like all insects, are arthropods, meaning their “skeleton” is on the outside of their body. To grow, they have to shed their outer casing (this is also the case for crabs, for example). But cicadas are very public about this because of their timed, large emergences, meaning you might notice hundreds of casings on the trees around your home.

Right after molting, the cicada is soft and almost colorless. This state in the life cycle of a cicada is called teneral.The cicada can actually look quite beautiful at this moment — white and green, instead of the dark wings and body with red eyes we’re used to seeing.

While you might be creeped out by the cicada cases or the large insects themselves, it’s important to remember that cicadas do not spread disease, bite, or sting humans. They are entirely harmless, except to some trees, of course. But they could be poor flyers and might accidentally bump into you!

Pesticides are not a good method of controlling cicada broods and are far more likely to damage your garden by killing off beneficial insects. During an emergence, there are so many cicadas that pesticides are unlikely to be effective. Netting or protective wrap for delicate trees is your best option for protecting against annual and periodical cicadas.

So come this spring, don’t panic when you start seeing and hearing cicadas around the garden. A double emergence like this one is special, especially if you have the eyes to see and the ears to hear.