Home / Blogs / Brood X: Return of the Cicadi
May 24, 2021
Brood X periodical cicada adults gather after 17 years underground (Photo scientificamerican.com).
A long time ago, in a forest not that far away, a small insect tunneled toward the soil surface. This insect had just spent its entire life underground, waiting for the right moment to emerge. When surface conditions were just right, this insect climbed a nearby tree and shed its exoskeleton. It then emerged as a fully-winged adult, flew off to mate, laid eggs, and died. But it was not alone. It was joined by billions of its brethren, emerging en masse for a spectacular event that only occurs once every 17 years.
The year was 2004, and I was a college undergrad working my first summer field job in Berks County, Pennsylvania. I vividly remember the deafening sound. The piles of dead insects on the forest floor. The pelting on my truck’s windshield as I drove through swarms of them. As a twenty year old, it was something I had never witnessed. They were cicadas, but not the cicadas I was used to hearing and seeing each summer. They looked and sounded different. And there were TONS of them.
They were periodical cicadas. Unlike the annual cicadas we hear and see each summer, periodical cicada species take part in a synchronous emergence that only occurs once every 13 or 17 years. In 2004, the spectacle I had witnessed was a result of the emergence of Brood X, or ‘The Great Eastern Brood’, a group of cicada species that emerge in synchrony once every 17 years. Since I couldn’t remember their previous emergence in 1986 (I was 2), witnessing this event for the first time was an incredible experience. I have thought about that experience many times since, patiently awaiting their return. The sheer numbers, prevalence, and sound produced by this brood is truly one of nature’s great spectacles. So get ready. After 17 years, the ‘children’ of 2004’s Great Eastern Brood are set to make their triumphant return to the fields and forests of the Chesapeake Region.
We categorize cicadas into two groups, annual cicadas, and periodical cicadas. Annual cicadas emerge every summer and include a number of different species. While their life cycle can take multiple years to complete, (the name annual is somewhat of a misnomer) at least some adults emerge every summer. These are the cicadas we are most familiar with. We associate summer with the buzzing chorus of these annual cicadas. We observe (and if you’re anything like me, still collect) their nymphal exoskeletons clinging to tree trunks each summer. These annual cicadas spend 2-5 years underground as nymphs, and it is here that they will feed on fluids in the xylem of plant roots in their burrows or chambers. During their time underground, cicadas go through multiple instars (developmental stages between molts) before they complete their larval journey and emerge as sexually mature adults.
Brood X nymphal exoskeletons on sweet gum (Liquidambar styraciflua) in eastern Virginia, May 2021 (Photo courtesy of Katie Hracho).
Each summer, these cicada nymphs emerge from the ground and shed their exoskeletons, morphing into winged adults. They live as adults for only a few weeks, during the ‘dog days’ of summer. Interestingly enough, one of the species of annual cicadas common in the Chesapeake region is known as the dog-day cicada (Neotibicen canicularis). During this time, males can be heard throughout the warmest parts of the day, producing one of the most iconic sounds of summer. To attract females, males produce a loud, almost ‘electronic’ sounding buzz. It starts out as a soft, almost ‘fuzzy’ buzzing sound. The buzzing quickly picks up pace and culminates in a rapid, repetitive crescendo that is almost deafening. Most insects use a method known as stridulation to produce sounds. This involves rubbing one body part (often a wing or leg) against another body part. However, male cicadas produce their sounds by using a unique sound-producing structure on their abdomen called a tymbal. These tymbals are formed by modified membranes that vibrate against a corrugated rib-like area on the cicada’s abdomen. The body then acts as a resonance chamber, amplifying the sound. Cicadas are one of the loudest species in the insect world, capable of producing sounds of more than 100 decibels!
After breeding, female cicadas cut slits into the bark of twigs and small branches where they deposit their eggs. The tiny cicada nymphs hatch from their eggs and fall to the forest floor, where they burrow into the soil to begin their life cycle again. Periodical cicadas employ a very similar strategy; the only catch is just how much time they spend underground as larvae.
Periodical cicadas are further divided into groups or broods that are based on their 13 or 17 year emergence cycle. Brood X, or The Great Eastern Brood, is comprised of three species that emerge every 17 years. What makes this ‘brood’ so interesting is that it is one of the largest in both geographic range and abundance. Brood X cicadas will emerge throughout most of the eastern United States and portions of the upper Midwest where suitable habitats exist (about 15 states). Periodical cicadas emerge somewhere almost every year, but they are comprised of different broods with varying geographic ranges. The emergence is synchronized within each brood, but not with adjacent (or even overlapping) broods. But regardless of species and distribution, all periodical cicadas spend 13 or 17 years as nymphs underground before emerging. The most recent brood of periodical cicadas that I witnessed was the emergence of Brood II (The East Coast Brood) in portions of the northeast in the summer of 2013. Brood II also consists of 17-year cicadas, and will emerge again in 2030. While this brood was locally abundant, it pales in comparison to the sheer numbers we are about to witness when Brood X emerges.
Periodical cicadas look and sound different than the annual cicadas we see each summer. The periodical species are typically smaller in size, with black bodies and distinct bright red eyes. Most annual cicadas are black and green with jet-black eyes. Periodical cicadas also sound different. They produce a buzzing sound that almost sounds like a monotone hum. The periodicals will also emerge before the annual cicadas, but there will likely be some overlap.
Adult periodical cicadas from Brood II gather to mate in 2013 in Schuylkill County, Pennsylvania (Photo Jim Kauffman, Alliance for the Chesapeake Bay).
Some aspects of the periodical cicada emergence are still not fully understood. However, it is believed that these species ‘count’ the years by somehow keeping track of the seasonal pulses of fluids within plant roots. After ‘counting’ 17 growing seasons, the cicadas begin their synchronous emergence when soil temperatures reach 65 degrees. They will begin to show up in southern states first, with the emergence slowly making its way north as soil temperatures rise. In early May they were already emerging in eastern Virginia. It is now late May and they are starting their emergence in southern Pennsylvania. But why such a long nymph stage? And why the need to emerge synchronously? While some theories for this life cycle are speculative, it is possible that this behavior evolved as a means of hiding from predators in both space and time. When cicadas emerge en mass, they ‘flood the market’ and overwhelm their predators. So many cicadas emerge that predators can’t possibly eat them all. They then ‘hide’ underground for another 17 years. If this emergence would take place annually, populations of predators would increase in response to an increased food supply. This could put more pressure on cicada populations and even potentially lead to more specialist predators. Avoiding predation by periodically flooding the market seems to have been an advantageous adaptation for these cicada species.
Periodical cicadas from Brood II gather on quaking aspen (Populus tremuloides) in 2013 (Photo Jim Kauffman, Alliance for the Chesapeake Bay).
Periodical cicadas will provide an incredible source of nutrients for many wildlife species. Birds will feast on emerging nymphs and adults. Many small mammals and even mesocarnivores will consume them. Herps, including snakes and turtles will feast where cicadas can be found. I am sure that large bullfrogs will devour any cicadas they can catch. Even fish will feed on expired adults as they enter the waterways of the Chesapeake. This emergence will offer anglers a once-in-seventeen-year opportunity to ‘match the hatch’ and try to fool our local trout by creating fly patterns that mimic periodical cicadas.
A periodical cicada imitator pattern developed for fly-fishing (Photo courtesy of (and fly tied by) Adam Miller, Alliance for the Chesapeake Bay).
Cicadas will even offer humans with a novel food source. Cicadas are both edible and palatable, and can be consumed safely by humans. Eating insects, or entomophagy, is a very common practice throughout many parts of the world. Insects provide an abundant source of protein in many cultures, and the stigma associated with eating insects here in the United States is often unfounded. Cicadas can be consumed in both the nymph and teneral stage. When the nymphs first emerge from the ground they can be collected and frozen to ensure they expire before molting. Once enough have been collected you can thaw and cook. The same process applies to the teneral stage, which refers to a cicada that has just emerged from its nymphal exoskeleton. In this teneral stage the cicadas are creamy white in color and have not yet hardened their final adult exoskeleton. The best time to find cicadas in the teneral stage is early mornings when the adults are emerging from nymphs attached to tree trunks (see photo below). They can be roasted, deep fried, boiled, or blanched depending on your preference. I for one can’t wait to grill up a Brood X Cicada Nymph Kabob. Or maybe deep fry a couple with some wasabi dipping sauce. Trying a few might be the part I am most excited about!
Adult periodical cicada (teneral phase) emerging from nymphal exoskeleton (Photo Tim Hudspeth, Alliance for the Chesapeake Bay).
Periodical cicadas are absolutely harmless. They do not bite or sting, and contain no toxins. The sheer biomass of shed exoskeletons and expired adults may be a nuisance, but their decomposing bodies produce nutrients that are recycled back into the ecosystem. It is possible that females laying eggs may damage a few trees, but the impacts should be minimal. Females cut small slits in the tips of twigs and branches to deposit their eggs, which may lead to localized damage on some trees. Evidence of this may be visible in areas where leaves are wilted and brown at the tips of tree branches. But most trees will recover.
Many wildlife species will feed on cicadas and may converge or congregate in areas where cicadas are extremely dense. I have seen articles circulating on social media that encourage ‘caution’ due to copperheads feeding on cicadas. While copperheads likely will feed on cicadas, this behavior should not increase the likelihood of human/copperhead interactions. Copperheads will feed on cicadas in habitats where populations of this snake already exist. Copperheads may spend a longer time in specific areas while feeding on emerging nymphs or expired adults, but they should not change their behavior or habitat use significantly enough to increase negative human interactions. However, it is certainly possible that this year’s increased food supply may lead to higher reproductive rates for copperheads in the short-term. But if you ask me, that’s a good thing, as copperheads are just as another treasure of our Chesapeake forests.
The term ‘Locust’ is often used by many folks to refer to cicadas. However, this term is not accurate. The term locust is used to refer to certain grasshopper species that have a swarming phase. Grasshoppers in the family Acrididae are typically solitary, but certain conditions will trigger them to become gregarious and congregate in vast swarms. During this swarming phase these grasshoppers are known by the colloquial term locust. The swarms move together, feeding constantly, devouring palatable vegetation (including human crops). Throughout history these locust ‘plagues’ have been recorded (and often feared) by humans throughout the world. The rocky mountain locust (Melanoplus spretus) was a species of grasshopper common in the western United States. This insect ‘plagued’ European colonizers as it swarmed and fed on farmers crops throughout western prairie states. When conditions triggered this gregarious behavior, this species formed vast swarms that included trillions. Incredibly, the rocky mountain locust has since gone extinct-a casualty of deep tillage and the conversion of grassland to row crops. It is likely that the term locust was incorrectly used to describe periodical cicada emergences as they appear periodically in vast swarms and may have reminded people of true locust swarms.
The pharaoh cicada (Magicicada septendecim) is one of three periodical cicada species that emerge as part of the Great Eastern Brood (Photo Ken Rosenthal/iNaturalist CC BY-NC).
Despite their extreme abundance, the future for cicadas does not come without challenges. Throughout history, even incredibly abundant species are not immune from human impacts. The passenger pigeon (Ectopistes migratorius) was once the most abundant bird on the planet. And it is now extinct. The rocky mountain locust numbered in the trillions, and it has also disappeared. In fact, some periodical cicada broods that were observed historically are now believed to be extinct, and no longer appear during emergence years. Intensive agriculture that impacts the soil directly impacts cicadas as nymphs. Suburban sprawl and development paves over countless nymphs living underground. Entomologists are also observing periodical cicada emergences in years when they are not ‘predicted’ to occur. Occasionally, members of certain broods will emerge in ‘off-years,’ often many years earlier than their historical pattern would predict. Is this a result of human landscape alteration, climate change, or natural variation? We aren’t sure yet. Either way, history has shown us that it’s important not to take common species for granted. Maybe take a longer look at the next robin or red-winged blackbird that you see, just in case. I’m sure some folks took billions passenger pigeons for granted, and now I would give anything just to see one.
I can not overstate just how incredible the spectacle will be. There will be areas where hundreds of thousands of cicadas will emerge in an area the size of an acre. This will include forests, fields, and even backyards in suburbia where the soil has not been disturbed. The nymphs will emerge from the soil en masse. Exoskeletons will cover tree trunks. Dead adults will pile up under trees. The noise will be deafening. It is truly one of nature’s great spectacles, and it will be happening right here in the backyards and forests of the Chesapeake. I encourage you to take some time to observe these insects closely, and appreciate just how special this event will be. Let your kids catch them. Collect a few and save them to show to your kids (or grandkids) before they emerge again in 17 years. Maybe even try to eat a few. My nephew is currently busy catching them in his Virginia backyard, and I look forward to helping him catch them again when he turns 19. See you in summer 2038!
Pennsylvania Forests Projects Coordinator
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