“Brood X”—the 17-year periodical cicadas—are emerging in May 2021. We expect the bugs to show up in big numbers in the next couple of weeks. Learn all about these fascinating bugs: where they’ll emerge, how long they’ll be here, telltale signs in your yard, and how to prevent any tree damage.
Cicadas are truly a fascinating phenomenon. This brood has spent 17 years waiting underground, will only emerge once to mate and lay eggs, and then the cicada babies (nymphs) fall to the ground to burrow back into the soil for the next 17 years! During this brief mating period, billions of fragile cicadas synchronize their emergence in order to overwhelm predators and secure the survival of their species. That loud noise? It’s the males singing a love “song” to the silent female! Yes, love is in the air.
What Are Periodical Cicadas?
During different years, different groups or “broods” of periodical cicadas emerge. There are 15 broods of periodical cicadas, which each appear like clockwork depending on their cycle. There are 3 broods that appear on 13-year cycles and 12 broods that emerge on 17-year cycles.
Brood X is the largest brood that occurs. That’s why it’s called the “Big Brood!” It consists of three separate species of periodical cicadas: Magicicada septendecim, M. cassini, and M. septendecula. They generally have red eyes and dark bodies measuring about 1-1/2 inches long.
Periodical cicadas are different than annual (dog day) cicadas, which appear every summer in far smaller numbers. In addition, cicadas should not be confused with locusts (which are grasshoppers).
We admit that screaming, red-eyed cicadas may look scary (or, cool?) but they only live to mate, lay eggs, and die.
Where Will the Cicadas Be in 2021?
In spring of 2021, entomologists predict that Brood X will emerge in 15 states as well as the nation’s capital:
As many as 1.5 million cicadas can appear in any given acre, however, numbers may be lower due to habitat destruction, fewer trees, and chemical use.
It is safe to say that if you had them in spring 2004 (when Brood X last emerged), you will be seeing them—and hearing them—again this year.
Some of our colleagues reported sightings of the “chimneys” in Ohio. And late April brought the first reports of cicadas starting to emerge in Tennessee, Georgia, and North Carolina.
There are two criteria which cicada nymphs or “teenagers” require to emerge in the spring:
The deep soil temperature (12 to 18 inches) reaches 64 degrees.
Often, a light rain often triggers theiremergence.
With the first reports of cicadas in late April, we expect more cicadas to show up the first week of May and then to see large numbers by the second week of May (starting May 10).
Emergence usually peaks around Memorial Day, but will depend on local weather conditions. The cicadas will be above ground for about a month before laying their eggs and dying off. The population begins to drop in June.
Telltale Signs That Cicadas Are Coming
If you’re preparing your garden soil in late April, you may end up digging up some cicadas that haven’t yet emerged. But you’ll know when the cicadas are about to invade by looking at your lawn for clues.
Look around under your trees and under rocks for small holes about 1/2 to 1 inch wide. They are often 12 to 18 inches deep. The nymph are already preparing their exit tunnels, ready to surface after spending 17 years underground. If it rains, these holes will disappear.
Sometimes you’ll see what are called escape “chimneys” or “turrets,” which are small tubes coming out of the soil; these are made in wet or muddy areas so that the water doesn’t just pour down the hole and drown the cicada.
Once the soil temperature is warm enough, thousands of cicadas will crawl out of the soil—usually under the cover of darkness—to “party” and find a mate. The nymphs will climb up a nearby tree trunk or shrub, seeking a safe spot to shed their outer skins or exoskeletons and emerge as adults. Similar to a human teenager, the cicada nymph needs to come out of his shell!
Within an hour, they become adults. Ten days later, the mating begins. The males will soon start singing to attract a mate. Once cicadas have successfully mated, each female lays up to 400 eggs in the twigs of more than 75 species of trees. Then the adult dies. When the eggs hatch, the tiny nymphs (about the size of a grain of rice) fall to the ground and burrow two feet into the soil, where they will live for another 17 years sucking on the sap from tree roots.
Scientists don’t really know how cicadas can count the years. One theory is that they have some kind of biological clock that’s tied to the trees.
How Long Do Cicadas Last?
Adult cicadas live for about 4 to 6 weeks. Depending on whether conditions and when they hatch eggs, the adults should die off mid- to late June. The dead adult insects will just drop to the ground. The eggs will start to hatch in 6 weeks, perhaps early August. The young immature nymphs will drop to the ground and bury themselves back in the soil. Brood X will next emerge in 2038.
Why Are There So Many Cicada All At Once?
Cicadas show up in the billions or even trillions to overwhelm predators and give their young a better chance of finding a mate and surviving.
Predators such as birds, fish, squirrels, reptiles, amphibians, insects, and arachnids gorge on cicadas when they arrive; cicadas provide increased food resources for many wildlife species and scientists see wildlife births rise after a periodical cicada cycle.
Cicadas make for very easy prey, as they’re not fast, do not fight, taste great, and are also nutritious! In fact, people all over the world eat these arthropods as a high-protein snack! (Shrimp, lobster, and crabs are also arthropods.) Dogs and cats love to eat these insects, too, but try to keep the pets from chowing down; the insects’ exoskeletons are not very digestible and could cause vomiting.
Are Cicadas Harmful to Humans?
No. They do not bite nor sting. Although the numbers of cicadas can seem overwhelming, they are not poisonous nor hazardous to humans or pets in any way. Their mouths don’t even have jaws. They are, in fact, a valuable food source for birds and other animals.
Cicadas do leave behind their shed casings on your patio or lawn, which can be a nuisance. Some folks will end up power-washing the casings away. Also, it’s fine to add cicadas to your compost pile or just let them fertilize the soil.
If they land on you, rest assured that it’s an accident and they’re actually looking for tree bark. If they are hard to brush off, it’s not because they’re attacking you; they have feet that are designed to grip onto bark. If they really bother you, do your outdoor chores when they’re least active (early in the morning and later in the evening).
What Does This Mean for Your Garden and Yard?
Let’s clear up one common misperception: Cicadas do NOT eat garden plants. We believe that many people are thinking of locusts, which are indeed incredibly destructive. In fact, cicadas do not eat at all! They may use their mouthparts to sip sap from trees just to stay hydrated, but adult cicadas do not eat. Their main purpose for the brief time they’re above-ground is not eating; it’s mating. (Talk about a cheap date!)
Healthy trees will withstand any egg-laying damage by the females, which cut small slits in pencil-sized twigs of deciduous trees such as apple, dogwood, hickory, or oak. If you see leaves at tips of branches turning brown (called “flagging”), this can be pruned away in winter or will fall away over time.
However, if you have very young trees or saplings, they do have a risk of twig damage. For that reason:
Avoid planting new or young trees until the fall or spring after emergence. If any damage to a newly-planted seedling does occur, it should sprout back from the root collar.
If you have a tree less than five years old, prune any damaged twigs the following winter. Also, damage from cicadas could result in multiple leaders; prune seedlings for one dominant leader.
If you have planted young trees or shrubs and are concerned about potential damage, cover with finely-woven netting or tobacco shade cloth with mesh less than 1/2 inch. Attach to the trunk or the cicadas will climb up the trunk to the branches.
NEVER spray insecticides, which aren’t effective and will only poison the wildlife that eats the cicadas.
In terms of the holes and mud chimneys in your lawn, most will disappear after a good rain. Or, just rake them over and add some grass seed. Your lawn will recover; in fact, the cicada’s digging helps aerate the soil and helps plant roots, similar to the way the earthworm works.
Image: Flagging due to cicadas. Credit: Dan Keck from Logan, Ohio. June, 2016.
How Do Cicadas Make That Loud Sound?
The males have a tymbal organ on either side of their abdomen that vibrates like a drumhead. The hollow abdomen amplifies the sound very effectively. It has been measured at 80 to 100 decibels, similar to a lawn mower, motorcycle, jackhammer, or jet flying overhead at 1,000 feet!
Do you have cicadas every year? There are annual cicadas that show up every summer but not in the great numbers of the periodical cicadas. In my area we have the Dog Day, Lyric, Canadian, and Say’s cicadas. To learn about your annual cicadas click on your state at the Cicadamania website.
Enjoy this very interesting video from 2004 which is the last time Brood X emerged. Who knew cicadas were so romantic?
The emergence of the periodical cicadas is a wonder of nature that will only occur a few times in your lifetime. Try to appreciate it while it is happening … and get some earplugs.