Should Gardeners Be Concerned About Cicadas?
No, not really. After 17 years, Brood X cicadas are set to emerge in 2021. Learn about these amazing critters and a few precautions you should take if they grace your yard.
Brood X cicadas (that’s ten, not x) are set to emerge this spring in parts of 15 states — Delaware, Georgia, Illinois, Indiana, Kentucky, Maryland, Michigan, North Carolina, New Jersey, New York, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia and Washington D.C. The last emergence of Brood X, a group of Magicicada on a 17-year life cycle, was in 2004. A lot has changed in the world since their last emergence.
In 2004, back when the only digital thing I knew was my digital clock, before my photographer husband and I had digital cameras, before social media platforms, before we used smartphones before we had broadband internet (we used telephone-based, dial-up internet back then) — before the digital world as we know it — I encountered the Brood X cicada emergence during a camping trip to West Virginia.
The amazingly loud, sustained buzz was noisy but more astounding than annoying. At first, we thought we might be experiencing some kind of engine trouble. On our way to a state park in West Virginia, winding around the back roads with the windows down, the loud, sort of electronic hum seemed omnipresent. We couldn’t tell where the rhythmic buzzing was coming from. And as we drove further into the forest, the hum became increasingly louder. When we arrived at our destination and saw the cicadas crawling up tree trunks, on rocks and other surfaces, we figured the collective song was coming from everywhere. We ran around looking for the different stages of emergence and picked up a few cicadas to inspect a little closer — red eyes, black bodies, and orange veins in their see-through wings. Observing the emergence was a wondrous experience.
Magicicada nymphs will crawl out of their underground tunnels and up a tree or other surfaces to find a location to begin molting into their adult form.
In Alabama, I am used to dog-day annual cicadas (mostly of the Neotibicen genus) with green bodies and black and brown markings. Life cycles vary from three to five years for our annual cicadas. With staggered life cycles, the cicadas emerge every year. The sounds male cicadas make by flexing their abdominal tymbals (drum-like organs) play a big part in the southern symphony made up of frogs, katydids, tree crickets and cicadas. The summertime chorus in Alabama is not unlike the insect chorus belonging to any other state, but the synchronous buzzing of Brood X cicadas is something different.
What does the loud noise mean? The males are basically singing, “Come over here. The clock is ticking. Let’s get busy before we die.” The female cicadas answer the call to action. They mate, and the female deposits her eggs in a groove she will make in a small-width tree limb. The grooves will serve to protect the eggs. The eggs hatch and the tiny, rice-sized baby cicadas (nymphs) will eventually crawl from the groove and drop to the ground where they begin tunneling into the soil to find roots to feed on. During the underground phase of life, they will undergo several molts, getting bigger and more developed each time. After 17 years of living underground, tunneling and feeding on xylem (plant fluid) of their host trees, Brood X cicada nymphs will emerge together in large numbers as soon as the soil reaches the right temperature (64 degrees Fahrenheit). They will crawl up plants or nearby structures, rid themselves of their exoskeletons (outer hard shells), pump haemolymph (insect blood) into their wings and harden their skin. While going through their final molt and transformation, the cicadas are almost completely white and turn to black as the skin hardens. The eyes are red, and the wings turn to orange. The red eyes make it easy to distinguish them from the annual species of cicadas. The most common species of annual cicadas are green and black.
During the final molt, the cicadas arch out of their cast exuvium (shells). At this stage, they are hardening their bodies enough to crawl out of the cast skins.
Ahead of the 2021 emergence, I contacted entomologist, Dr. John Lill, chair of the department of biological sciences at The George Washington University. Dr. Lill, his colleague, Dr. Martha Weiss from Georgetown University and post-doc Dr. Zoe Getman-Pickering are working on a multiyear project to examine how the Brood X periodical cicada emergence affects the function of the forest food web. Partnering with Diane Lill, director of the Green Kids program for Audubon Naturalist Society, the team put together a fun website chock full of digitally based education materials. The website includes a digital workbook, informational video, cicada art and links to websites and community science projects. Their goal is to build a network, educate children and prevent fear of these harmless insects.
I asked John a few questions about the emergence. Answers are edited for space.
Why 17 years? How do these cicadas tell time?
That is still a bit of a mystery. Seventeen years is a very long life span for any insect, and periodical cicadas are among the longest living insects on record. There are actually different species of periodical cicadas that are on 13 and 17-year cycles. One line of thinking suggests that having long intervals between successive emergences ensures that no potential predators can 'track' these cycles. There is some evidence that the seasonal changes in the quality of the xylem sap they feed on as nymphs (while underground) may be providing the 'information' they need to mark the passing of years, but how they keep track of the number of cycles is still a mystery! The synchronous emergence of millions of adults all within a few weeks clearly works to 'satiate' all available predators, ensuring that many will survive to reproduce the next generation.
While completing transformation, this adult male dries its body and wings so it can fly into the trees to escape predators the next morning. He will turn black with orange veined wings by dawn. Male abdomens are rounder and blockier, while female abdomens are slender and pointed.
Do they ever get their triggers or signals mixed up and emerge early or late?
Yes! When mistakes are made, and some portion of a brood emerge four years early (a common occurrence for 17-year cicadas which we observed for Brood X in 2017), they typically don't survive well and/or are in insufficient abundance to establish a 'chorus' (a large collection of adults that stimulates mating). Broods of 17-year cicadas often have a subset of individuals who emerge four years early, and that is potentially one way that the 13-year cicada species evolved. Also, there are often a smaller number of individuals that emerge a year early, which happened locally in the spring of 2020 (in my yard!). Both the four-years early and one-year early emerging insects are called 'stragglers' (even though they come out early). There are also likely some that emerge one year late, but that is less common.
How long will they live as adults?
The adults live a very short time, probably between three to four weeks on average, with many dying much sooner than that (predation, getting stuck while molting, etc.). Males are only interested in mating. The females need to fly off after mating to locate pencil-sized twigs on trees to lay their eggs in. Their ovipositor is like a small saw that they use to slice open twigs and they lay about 20 eggs in each slit. Each female will lay up to several hundred eggs in a series of these 'egg nests'.
Within five days after emergence, male cicadas sing, females answer with clicking, and mating ensues. The female will lay hundreds of eggs before she dies. And thus, the 17-year life cycle begins anew.
Should homeowners worry about plants in the garden that might be susceptible to damage from the cicadas?
The only thing to worry about is small trees and shrubs, which can be damaged from female cicadas making their egg nests. Landscapers recommend choosing not to plant new young trees and shrubs this spring until after the cicadas have completed their life cycles. If you have small trees that are a concern, you can purchase netting to drape over those plants to keep the females off of them. Larger trees are resilient and will survive just fine. The adults do not really feed on aboveground plants, so there is not concern for vegetables, flowers or herbs that people typically grow in their yards or gardens.
What insects and animals prey on the cicadas?
Almost any animal that CAN eat cicadas WILL eat them: many different species of birds, rats, mice, raccoons, opossums, squirrels, foxes, chipmunks and even fish. Also, dogs and cats will eat them readily, and if they eat too many, it can cause digestive problems.
With all of the basic information in mind, you may find more in-depth information at Cicada Mania. In the Brood X section, I found beautiful photographs and videos by researcher and enthusiast Roy Troutman, who was kind enough to lend pictures for this article. Also, on the website, you can find a timetable for emergence. Of course, weather and temperature will be a factor, but it is good to know what to expect and when.
After mating and egg-laying, cicadas will fall to ground and die. As summer sounds return to normal, there'll be dead cicadas and nymphal shells to clean up.
Other than cleaning up the exoskeletons and cicada carcasses, you need not worry about the cicadas' presence. They are not pests. You may need to sweep or rake them at some point to keep away from your pets, and to keep your outdoor living space tidy. And if you have a pool, take care to keep the carcasses from clogging the filter. Brood X emergence should be thought of as an extra cool natural phenomenon. Enjoy the show.