The Periodical Cicada*

by John Zyla


Maryland is fortunate enough to be geographically located in an area where many plants and animals terminate their ranges in the state either coming down from the north or coming up from the south. This has been one of the many reasons I have enjoyed studying Maryland’s varied flora and fauna over the years. I began as a birder when younger, and transitioned to a reptile and amphibian enthusiast (especially salamanders) in my teens and early twenties always looking for those rare species. Maryland has always been a great and varied place to study natural history…from the ocean to the mountains with the beautiful coastal plain and piedmont to complete the wonderful mix. Since 1996 however, I have become fascinated with a very well known, but very little understood insect (at least in our state). That year, I heard that a “Brood II” of the periodical cicada was about to emerge. As a naturalist with the Calvert County Natural Resources Division at Battle Creek Cypress Swamp, I was curious as what to expect and amazed at the lack of information on just where the cicadas were to occur in Maryland. I was fortunate to have a great group of volunteers at my disposal, so I began to map out where these cicadas were emerging that spring and the rest, as they say, is history!

The Periodical Cicada is actually a composite of 7 described species of insects belonging to the genus Magicicada. Four of these have been recorded from Maryland. The genus is divided into 2 groups, the 17-year periodical cicada and the 13-year periodical cicada. Magicicada is confined to the eastern United States and is found nowhere else on earth. They are not to be confused with the annual or dog-day cicadas that are found throughout our state from July through October. The periodical cicadas emerge in a small window of time from around May 20 to June 20 every 13 or 17 years depending on where you live in the state. They can occur before and after these dates, but this period tends to be the peak of their emergence.

Maryland can boast of 11 species of annual or Dog Day Cicadas. They get their name from the fact that they occur during the hottest days or “dog days” of each summer. Our annual cicadas vary in size from about a half an inch to almost 3 inches. Each species has its own distinctive call and males will emerge individually and usually sing by themselves. While every one in Maryland is familiar with the common summer time cicada calls that occur every year, they do not draw as much attention as they periodical cousins when they emerge after 17 years.

The life cycle of the periodical cicada begins as a small nymph that is hatched out on the twig where its mother had laid a series of eggs. Females can lay up to 600 tiny eggs. Within a month or two the hatchling young cicada will drop to the ground. After burrowing in through the dirt, the young cicada nymph will choose a root that it will use to feed on for the next 17 years. Cicadas have a straw like mouth part that allows them to “drink” or “suck up” sap from tree roots or branches. Then progressively over those years, the nymph will grow in size until it is ready to emerge. In late April or early May of the seventeenth year, the nymphs will begin to burrow out of the ground and construct tunnels to the surface when the temperature of the soil reaches 64°. This is all in anticipation for the grand finale. By May 20, most of the nymphs have emerged from the ground, crawled up a tree or other vertical surface and have emerged from their cast skins. After emerging the adult cicada is all white except for two black areas on its back that are thought to mimic “eyes” to avoid predation. At this stage they are soft and very vulnerable, just like a soft crab before it hardens. The cicadas generally emerge at night, again to avoid predators, and harden through the night until they become the black bodied orange-eyed insects with which everyone is familiar.

When the adults have fully hardened they are ready to make the ascent to the highest point in the area and begin the deafening chorus to attract mates. Only the males can call as the females are silent. As the males congregate and produce a louder and louder call, females are attracted from the surrounding area. Unfortunately for many cicadas, after 17 years underground they may miss the big party. Due to getting stuck in their sheds, falling to the ground, getting eaten or being inflicted with a fungus that replaces their reproductive organs, many cicadas never get to enjoy the fruits of their labors. For those that do make it, the party goes on for about a month. During that time the females will lay their eggs in the small twigs at the end of branches by cutting a slit with a specially adapted ovipositor that “saws” a cut into the chosen twig. The eggs are laid and the cycle of life begins again. All the adults have usually died and fallen to the ground by July. The great commotion is soon over and silence will reign again until 17 years later.

Now, to make things more complicated, not all periodical cicadas come out at the same time throughout the eastern United States. While all populations are synchronous with each other (either 13 or 17 years), each group may emerge at different times from one another. Each group that emerges together during the same year is called a “Brood”. Potentially, there could be 17 broods (one for each year) of 17-year cicadas and 13 broods of the 13-year cicadas. In actuality, researchers have confirmed that there are 12 broods of 17-year cicadas and only 3 existing broods of 13-year cicadas. In 1907, C. L. Marlatt, an Entomologist at the U. S. Department of Agriculture proposed designating each brood with a Roman numeral. He designated the brood that occurred in 1893 as Brood I and continued the numbering system each succeeding year. This numbering system has been universally accepted ever since.

In Maryland, our big (largest in size geographically) brood is Brood X. It is also the brood that can be traced back the farthest in history. Various newspaper reports can be found from the 1700’s and 1800’s regarding this brood in Maryland. In 1902, A. L. Quaintance published an article describing the Maryland distribution of Brood X by soliciting replies from each post office in the state. He sent out a questionnaire regarding whether periodical cicadas were occurring in the vicinity that spring. This was therefore, the first brood documented in Maryland.

In 1996, Brood II emerged in St. Mary’s, Calvert and Charles counties, but not throughout the area. The heaviest concentration appeared to be confined to the area from Lexington Park north to Golden Beach in St. Mary’s County, (but not along the Potomac River) and northward to Chaneyville Rd in Calvert County and south again to Prince Frederick, but not including Plum Point area. Through the help of the volunteers at the nature center, the entire range of these cicadas was mapped out. Every woodlot where they were known to occur or not to occur in the three counties of Southern Maryland was carefully mapped out. Again, most of Charles County seemed to be devoid of any periodical cicada emergence even though the soil and vegetation types are similar. This 20-mile gap between the then emerging Brood II and the historical distribution of Brood X that last came out in 1987 was an unexpected discovery in mapping out these cicadas.

In 1998, a local resident presented me with a live male periodical cicada in May. Knowing that Brood III was confined to the mid-western states, I was puzzled at first. It slowly dawned on me that I was about to confirm the first documented occurrence of Brood XIX of the 13-year cicada in the state! I mapped out the area of occurrence which ended up being just 5 miles long by one mile wide from just below Lexington Park, St. Mary’s County to just north of Ridge, in the town of Dameron. I sent specimens and recordings to the University of Michigan, Museum of Zoology (UMMZ) which confirmed their identity. This is the northern most locale for 13-year cicadas in the eastern United States. This small relict population which is adjacent to Brood II from the north will be an interesting population to study the next time they emerge in 2011. Why a relict population has survived completely cut off by water from the main body of the brood is a still a mystery.

In 1999 my family headed to Garrett County, Maryland to meet up with a Maryland Public Television crew to see if we could find and document Brood V in the far northwestern corner of the state. The emergence was very localized and was not county wide. It was interesting how this brood emerged in a very definite area. As we drove around the edge of the emergence, one mountainside with no apparent change in vegetation was silent, while as we crested the next mountaintop that familiar sound was very obvious! There was also a gap between where Brood X historically was found and the presence of Brood V. This gap has not been fully explained.

This distinctive line where broods chose not to cross or are limited to has intrigued me enough to study these insects for the past few years. My only problem is that I have to wait 17 years between emergences in order to map out their distribution!

So what can we expect from this year's emergence of Brood X? If you live within the area shaded on the map of Maryland, chances are you will definitely know when the cicadas emerge. Typically around the 20th of May the chorus of the periodical cicada becomes noticeable. Many describe it as a “humming spaceship sound” coming from the nearby woodlot or above from the trees in your yard. These cicadas are perfectly harmless. The worst they can do is accidentally fly into you. The only damage the cicadas may inflict is on newly planted orchard trees or drowning out a graduation or wedding ceremony.

If you are interested in obtaining further information, probably the best site on the web is the UMMZ site. I hope to have my new web site, www.cicada.info, on-line sometime in April. If you have periodical cicadas emerging at your home, work, or at a relative's or friend's house, please consider filling out a field form describing the location. And even if you do not have the cicadas emerging, please fill out the form anyway–even negative records are very helpful.

While many people fear the emergence, I believe it’s a great time to reflect on such a natural wonder that is with us such a short time.

*This article was published in the Summer of 2004 prior to that year's emergence.