Questions about what to expect when it comes to the periodical cicada emergence of 2024? Tom Tiddens, plant health care supervisor at the Chicago Botanic Garden, helped out with answers.

When should we expect to see and hear the periodical cicadas this year?

Periodical cicadas are estimated to emerge around May 15 to 30 and stay active through June—but their emergence is weather-dependent; given the warm winter, we could be looking at emergence on the early side. They’ll come out when the soil temperature at 8 inches deep reaches 64 degrees Fahrenheit. Hard to say exactly when that will happen! When it does, a nice warm day will trigger them to come out.

In a given area, most cicadas will emerge over only a two- or three-day period, which is an amazing sight. Once they’re out, they make a lot of noise, which at peak levels can be as loud as a lawn mower. They mostly sing between 10 a.m. and 5 p.m.

Where will we see the most cicadas?

Cicada levels will be highest in areas adjacent to woodlands and in older neighborhoods; disturbed lands limit their numbers greatly. Also, researchers have estimated that in a woodland area, as many as 1.5 million cicadas may emerge. That’s a lot!

Will we still have the annual cicadas this summer?

Yes, annual cicadas (aka “dog-day cicadas”) are a different species and will still show up this year, during their usual period from July to September.

What’s the difference between periodical cicadas and annual cicadas?

Periodical cicadas are black with orange wing veins and red eyes, about ¾ to 1¼ inches in length; annual cicadas are green with black eyes and on the larger side, approximately 1 to 2 inches long.

Another thing that differentiates the species is that annual cicadas have a two- to five-year life cycle, with some emerging each season. That means they mature at different times, which is why we see them every year; they are not synced up like the periodical cicadas.

Why is this emergence so unique?

This periodical cicada emergence is special because Brood XIII (a 17-year periodical cicada type) and Brood XIX (a 13-year periodical cicada type) are emerging in the same year; the last time this happened was 221 years ago, in 1803.

Where can you see the different broods?

A brood represents a geographical/regional area where a large grouping of cicadas are on the same emergence schedule. Broods to the south are on a 13-year cycle, and broods to the north are on a 17-year cycle. The dividing line between 17- and 13-year broods is right around the center of Illinois—so Northern Illinois is part of the territory for Brood XIII, which also shows up in parts of Wisconsin, Iowa, Indiana, and Michigan; they last emerged in 2007. Southern Illinois hosts Brood XIX, the 13-year brood, which touches 14 states total. This means that the entire state of Illinois will see periodical cicadas emerge this year. This doesn’t mean twice the cicadas, though; small areas where the broods overlap could see the highest numbers, but in most regions, like the Chicago area, only one brood is present.

What’s the life cycle of a periodical cicada?

Juvenile periodical cicadas (nymphs) develop underground throughout their 13- or 17-year cycle, feeding on fluids from plant roots. A few weeks before emerging, they construct a ½ inch-diameter exit tunnel; their emergence is closely synchronized, with most nymphs emerging the same night or within a few days. They come out around sunset and climb up a nearby vertical structure, like a tree or shrub, to complete their final molt into adulthood as a winged cicada. You’ll often find the exoskeletons (shells) from their final molts on tree trunks.

Newly molted adults have yellow-white skin that darkens as their wings and body harden over four to six days; adults are about 1¼ inches long, black, red-eyed, orange-veined, with clear wings, and they live for two to four weeks.

Male cicadas attract females for mating by singing (vibrating their tymbals—drum-like muscles on their abdomens). Different species produce different songs. Females don’t have tymbals, so they’re not the ones making noise.

After mating, females find twigs ranging from ¼ to ½ inch in diameter to lay their eggs. The female uses her ovipositor to create a series of longitudinal slits in twigs and lays up to 20 eggs in each slit. Each female will lay about 600 eggs.

In six to ten weeks, eggs hatch and small nymphs are born; these newly hatched, ant-sized nymphs drop to the ground and burrow 6 to 18 inches to find a suitable root to feed on for nearly 17 years (in the case of Brood XIII), until they’re ready for the next emergence.

What role do periodical cicadas play in the ecosystem?

Periodical cicadas are difficult to study because people will only witness about four life cycles of the 17-year cicada in their lifetime, so it’s hard to learn the long-term effect on the ecosystem. What we do know is that when they emerge, they temporarily disrupt the food chain, because they become a food source for many other animals—pets, rodents, marsupials, reptiles, birds, fish, insects, arachnids, even people. The result of this disruption may be an increase in other insects, as predators (like bats) may favor the big easy meal of a cicada over their normal tiny insect meals.

Are people and pets safe? (Yes!)

Witnessing the mass emergence and cicada activities might seem a bit eerie, but it’s a fascinating phenomenon that shouldn’t be missed—and these insects won’t do you any harm. They are non-toxic to people and pets, so don’t worry if your dog eats them. If you’re feeling adventurous, you can even find recipes online. They do not bite or sting and won’t hurt you or your pets in any way.

Are plants safe? (For the most part, yes!)

Adult cicadas can damage small tree branches and feed on plant leaves, but most trees will tolerate the damage without a problem, and the leaf damage is very minor. Damage from adult cicadas is mostly in the form of small branch die-back; females make longitudinal slits in pencil-sized branches to lay eggs, and that branch might break or die off from that point outward. This is called flagging, and you may see brown branch ends, sometimes hanging, later in the season. Again, most trees won’t suffer much from this. The damage is only really concerning on smaller trees with mostly small branches.

As for nymphs that feed on plant roots for years before emerging, the damage to roots isn’t thought to affect the plant much.

Is there anything we can do to protect our small trees?

Consider protecting small high-value trees by wrapping them in a fine mesh (such as tulle), and delay planting new trees until after cicadas have completed their emergence. We do NOT recommend using insecticides for cicada management.

Is there anything important to know or keep in mind besides the noise?

Keep in mind that this is an incredible natural occurrence; get outside and experience it—there’s nothing to fear from periodical cicadas. This opportunity won’t come along in the Chicago area for another 17 years, and it will be 221 years until another double brood emergence happens. It’s an awesome opportunity to witness a unique natural wonder.    
 

Get more information about periodical cicadas here.