The term “brood” is applied to the massive synchronous appearances of periodical cicadas and Roman numerals are used to define both the year and the geographical distribution of each emergence. Thus far, researchers recognize 12 broods of the 17-year cicadas and 3 broods of 13-year cicadas in North America. Most broods are concentrated from the Mid-Atlantic states across to the eastern edge of the Great Plains.
Two broods are now considered to be extinct. Brood XI (11) was last observed in 1954 in eastern Connecticut. Brood XXI (16) was recorded in the Apalachicola River Valley in Florida but has not been observed there since 1870.
Brood X (10) of the 17-year periodical cicada is one of the largest based on geographical distribution. It will rise from beneath deciduous trees this spring in parts of Ohio as well as Delaware, Georgia, Illinois, Indiana, Kentucky, Maryland, Michigan, North Carolina, New Jersey, New York, Pennsylvania, Tennessee, Virginia, West Virginia, Washington D.C.
BYGL readers in Ohio may be justified in thinking, “here we go again.” The Buckeye State periodically “enjoys” the appearance of four different broods of 17-year cicadas and one brood of the 13-year cicadas. It’s an entomological twist on our state’s tourism slogan, “Ohio. find it here.”
The 13-year Brood XXII (22) last made an appearance in the southern part of Ohio in 2014. The 17-year Brood V (5) emerged in the eastern part of the state in 2016 and Brood VIII (8) regaled Buckeyes in the extreme northeast part of the state in 2019. Parts of southern Ohio including eastern Hamilton County will revel in cicadas again in 2025 with the appearance of Brood XIV (14). Ohio is a great place to be an entomologist!
Prepping for (Socially Distanced) Cicada Parties
Cicadas (family Cicadidae) are sucking insects and resemble huge aphids (they are related). All cicadas develop through their immature stages (nymphs) deep within the soil where they use their piercing-sucking mouthparts to tap into tree roots. However, this feeding activity has never been shown to cause significant harm to overall tree health.
So-called annual dog-day cicadas (Neotibicen canicularis) appear sporadically throughout the “dog days” of summer usually beginning sometime in July. Although it takes 2-3 years for dog-day cicadas to complete their development, some adults emerge every year due to overlapping generations. Thus, they have been incorrectly labeled as an “annual” cicada.
The cicada killer wasp (Sphecius speciosus) is the nemesis of dog-day cicadas. The wasp measures 1 1/8 to 1 5/8″ in length and is one of the largest wasps found in Ohio. Cicada killers feed exclusively on annual dog-day cicadas; they do not prey upon periodical cicadas. The synchrony with annual cicadas makes sense if you consider that the wasps would starve to death waiting 13 or 17 years for a periodical cicada meal. So, the large numbers of periodical cicadas this spring in Ohio does not mean there will be a bumper crop of cicada killer wasps.
“Periodical” applies to cicadas that require 13 or 17 years to complete their development. Adults emerge en masse in the spring, usually beginning in early May, sometimes in late April, and ending sometime in June.
Their emergence is preceded by the appearance of holes beneath trees which are sometimes surrounded by mud “chimneys.” The holes are beginning to appear in southwest Ohio and may be observed by pulling away leaf litter.
Brood X includes three species: Magicicada septendecim, M. cassini (= cassinii), and M. septendecula. These species are typically asynchronous in their emergence. Thus, there may be an observable rise and fall in the number of cicadas clambering around Ohio’s forests and landscapes as the different species emerge.
The cicada offensive begins with cream-colored adults wrapped in their nymphal exoskeletons crawling from the soil onto any handy vertical surface (e.g. trees, shrubs, grass, fence posts, slow-moving gardeners, etc.). They may look like cicada nymphs, but their true identity is revealed by their red eyes.
Soft-bodied, light-colored (teneral) adults emerge through a split (ecdysial suture) on top of the nymphal exoskeleton; the process is called ecdysis. The teneral adults pump fluid into wing veins to extend their wings and their exoskeletons harden and acquire the final coloration. Then the fun begins.
Eventually, the cicadas will take flight, and males begin to “sing.” The males have two structures on their abdomens just behind the wings called tymbals. The tymbals are constructed of a thin membrane connecting thick “ribs.” You can see the ribs in the photograph below.
The cicada uses strong muscles inside their bodies to pull the tymbals inward causing the ribs to buckle which makes a sharp snapping sound. Another sound is made when the muscles relax causing the tymbals to snap back. The cicada repeats this action 300 to 400 times per second to create a vibrato drone. The sound waves from the two tymbals are equal in frequency and amplitude allowing the two waves to come together; a phenomenon called superposition. This causes the amplitude (= sound volume) to increase. Songs of individuals are further augmented by a synchronic orchestra of tens of thousands. The sound has been measured at over 100 decibels which is equivalent to listing to a revved-up chainsaw held at around three feet from your ears.
Of course, the cacophony is music to the “ears” of a female cicada and ultimately brings her to a mating meeting. Once mated, female cicadas use their spade-like ovipositors to insert eggs through the bark and into the white wood of small branches and twigs. The resulting damage splits the bark and white wood leaving deep furrows of ruptured tissue. The oviposition (ovi = egg) injury often causes stems to die; the leaves turn brown (“flag”), and the damaged stems detach and drop to the ground.
Stem detachment is actually a good thing for the nascent cicadas. The soil is the ultimate destination of the first instar cicada nymphs that hatch from the eggs. Once in the soil, they migrate to tree roots where they attach themselves to sip the essence of root for the next sixteen years.
If the damaged stems detach and drop to the ground before the eggs hatch, the nymphs can just step off right onto the soil. Otherwise, the nymphs must take a leap of faith. Nymphs that hatch high up in tree canopies may drift down to the soil or they may be blown off course perhaps onto a midnight train to Georgia never to be seen or heard from again.
However, sometimes the damaged stems do not detach, and flagging remains evident throughout the fall. Likewise, oviposition slits may also remain evident throughout the season and even over multiple seasons creating a diagnostic challenge for several years.
A Word About Management
It’s important to keep in mind that periodical cicadas co-evolved with their hardwood hosts. They are not tree-killers. Their damage to established trees is minimal. Indeed, their focus on the tips of branches and twigs translates into a form of “natural pruning.”
We’re often asked, “what good are cicadas?” The short answer is that they are an important part of eastern deciduous forest ecosystems. Research is just scratching the surface regarding the ecological services provided by periodical cicadas; however, we know that they make up for the small amount of damage caused to their host trees by stimulating fuller canopies through tip-pruning. They help with new root development by aerating the soil and their decaying bodies return nutrients to trees.
They are also eaten by a wide variety of insectivorous animals from raccoons to bears as well as birds. Indeed, one reason periodical cicadas appear in such huge numbers is use “predator satiation” to minimize the overall impact from predators. Their sheer numbers simply overwhelm even the most gluttonous predator leaving large numbers to reproduce and ensure the survival of Magicicada spp. Of course, the downside is that domestic dogs and cats may gorge themselves into earning a trip to a veterinarian. Keep an eye on your pets!
In most cases, management of the periodical cicada is not necessary. As noted, they have a limited impact on established trees and shrubs. Also, populations are often highly localized. If you didn’t see them in your landscape in 2004, it’s unlikely you’ll see them this spring. If your home was built on land that was a crop field, periodical cicadas didn’t become established. If you live in a housing development that was carved out of a forest, but the soil was extensively excavated and moved around, it’s likely the cicadas were destroyed. Periodical cicadas must have trees and they typically don’t fly far from the trees from which they developed.
Of course, fruit trees and newly transplanted landscape trees may need to be protected from oviposition damage if they’re located near a forest or in landscapes with a past history of periodical cicadas. Ovipositon wounding on small trees can be prevented by covering them with nylon netting with a mesh size no larger than 1/2 inches.
However, netting trees should be reserved for locations where there is a clear and present danger from periodical cicadas. That’s because new growth may become distorted by the netting. Also, tightly packed foliage creates a microenvironment conducive to foliar disease development. It is recommended that homeowners and landscapers delay netting until they see the red of the cicada’s eyes. A cicada emergence starts off slowly, so observing cicadas before covering trees with netting will justify the risks associated with using the netting.
Insecticides are not generally effective against periodical cicadas. They are sucking insects meaning they won’t consume insecticides applied to stems and foliage and they are large insects requiring a high dosage. Also, topical insecticides may kill beneficial insects important for keeping other pests in check. A cicada application this spring may translate into dealing with more serious pests later in the season.
Finally, periodical cicadas focus their attention on deciduous hardwoods; they are not a conifer pest. Although desperate cicada females may be observed oviposition on a wide range of non-preferred hosts including pines, the result does not bode well for the nymphs. We can only imagine nymphs muttering, “what was mom thinking?” as they try to free themselves from sticky pine resin.
Myths and Mythconceptions
Periodical cicadas are not locusts. Locusts are grasshoppers. The mistaken identity originated with early European colonists who had never seen cicadas before or the Biblical locust plagues for that matter. However, the mass emergence of a periodical cicada brood appeared like something straight out of the pages of Exodus (10:1–20).Interestingly, the “weeeee-whoa” song of M. septendecim is sometimes described as sounding like “Pharaoh” no doubt adding further weight to the mythconception.
Although cicada females have long sucking mouthparts, they will not plant their proboscis into the arms of horrified gardeners. Likewise, they will not use their long, sharp, wicked-looking ovipositors to “sting.” People aren’t at risk unless they look like an oak tree.
Join the Cicada Safari Team
Although much is known about periodical cicadas, there remain many unanswered questions. Most importantly, the exact geographical distribution of Brood X including locations within the historical range needs to be further defined. As noted above, cicada populations are often highly localized with large concentrations commonly near areas with no cicadas. It’s important for future predictions to better define where we do and don’t see periodical cicadas.
Gene Kritsky (dean of Behavioral and Natural Sciences and professor in the Department of Biology, Mount St. Joseph University, Cincinnati) worked with the Center for IT Engagement at Mount St. Joseph to develop an easy-to-use smartphone mapping app. The free app can be download from the Apple App Store or Google Play. It allows observers to photograph cicadas and submit the pictures so sightings can be confirmed and added to the cicada map.
I strongly urge that you download the app (see the hotlink below) and use it to help us learn more about Brood X. Become part of the Cicada Safari!
Click on the hotlink below to access the Cicada Safari website https://cicadasafari.org/