Jon Zawislak, Assistant Professor – Apiculture and Urban Entomology
Austin Jones, Instructor and Director of Undergraduate Education

A bunch of bugs have become this season’s newest newsworthy celebrities based on the astronomical numbers expected to appear. Over the next couple of months, people in the South will witness the emergence of the largest brood of periodical cicadas in the country, spanning parts of 16 states. These cicadas have been literally lurking silently under our feet for the last 13 years, and are now beginning to make their voices heard for the first time. 

The insect army poised to invade are still nymphs, in the very last stage of their development. After feeding on fluids from tree roots for 13 years, slowly growing and molting underground, they will make their debut by crawling up and out of the soil when it warms to about 64°F and is softened by rains. These nymphs will make their way up onto vertical surfaces, such as trees, fenceposts and houses, where they will pause for a rest while their exoskeleton splits open. The fully formed adult cicada will crawl out and leave its hollow cast shell behind for us to see.

Magic cicadas?

These insects are known as periodical cicadas, due to a lengthy gap between the adult populations. They are part of a species complex in the scientific genus Magicicada, a name that emphasizes the sudden appearance and disappearance of so many bugs. Early colonists in the new world may have likened their sudden manifestation to a biblical plague, resulting in the common misnomer of “locusts” – a term that is accurately reserved only for grasshoppers migrating in large numbers. 

Scientists who study cicadas group their populations into “broods” based on when they are expected to appear, and designated by a roman numeral. The cicadas emerging across the south right now are part of Brood XIX. Their life cycle takes 13 years to complete, which is why they are known as 13-year cicadas. To add to the confusion, Brood XIII, which has a 17-year cycle, is poised to emerge this spring as well.  However, this brood is restricted to a handful of northern states. The two broods are only likely to overlap geographically in southern Illinois and Indiana. The last time this occurred was 221 years ago, coinciding with the Louisiana Purchase in 1803.

Getting Together

Individual cicadas will only live about 4-6 weeks. And that’s if they are lucky. These bulky bugs are a prime source of protein-rich food for many other animals. Birds, bats, frogs, fish, raccoons, lizards, snakes and even bears will feast on this abundant buffet. Many spiders and other insects will also get a meal. Even fungi grow on a few unlucky cicadas. Whatever the cause of their demise, their remains will add a layer of fertilizer to the surface of the soil, returning those nutrients to the trees that fed them as nymphs.

The abundance of hungry predators seems to be exactly why the cicadas have evolved such an incredible synchronized mass emergence. By simultaneously appearing in potentially millions per acre, the community of predators becomes overwhelmed with abundant food and soon has their fill. Anything that might eat a cicada will soon stuff themselves before they can possibly eat them all. That leaves the rest with better odds to survive and complete their single task of reproduction.

Male cicadas climb up into trees and begin calling out with their familiar loud songs to let females in the area know they are available. Their exoskeletons feature ribbed membranes, called tymbals, which can click back and forth more than 300 times per second. Hollow chambers in their abdomen help to amplify this sound, while their wings can be angled to help direct the sound waves. Males often gather in groups, called choruses, to really turn up the volume. Why? Because the males with the loudest calls are presumably the largest, strongest and healthiest, and presumably perceived to be the best choices for mates, which in turn attract the most females. Arkansas is home to more than 20 species of cicadas. The brood currently showing itself is a complex of four species: M. tredecim, M. neotredecim, M. tredecassini, M. tredecula. While their songs may sound essentially the same to us, they can tell the difference. 

Male cicadas typically emerge a little sooner than females, eager as they are to begin the final phase of their life cycle. However, the earliest members of the cohort are also the most likely to be eaten before predators are satiated. For cicadas, it pays to be fashionably late to this party.

Life Cycle

After mating pairs find each other, and a brief courtship ensues, the female cicada uses her ovipositor to saw a shallow crevice into a tree branch, where she deposits up to 20 eggs. She will repeat this process, producing up to 600 eggs over 3-4 weeks. 

After about 6 weeks, the eggs hatch and the nymphs drop to the ground. Because they are so small, they are not hurt by the impact. They quickly burrow into the soil and will tap into plant and tree roots to feed on the xylem almost right away. They will continue to feed like this, sometimes moving to new food sources as they slowly mature. The nymphs will grow and molt four times over the next 13 years, when it will be time for the next generation to emerge. 

It's not uncommon for a few individuals with quicker metabolisms to emerge a year early, or even a few stragglers to emerge a year late from the rest of the group. However, these have poor odds of finding a mate on the same schedule, and will have much higher odds of being found by something looking for a meal. These pressures tend to keep the majority on the same schedule.

What should you do?

Homeowners may be wondering how to prepare for this impending invasion of six-legged noise machines. Are they dangerous to people, pets, or plants? While large and noisy insects may be intimidating to entomophobes who are already creeped out by small crawly things, cicadas are not venomous and can’t sting. Mature adults don’t feed and don’t even have functional mouthparts with which to bite. Having spent the last 13 years doing little more than eat, they emerge with the single-minded goal of making more cicadas. 

Cicadas themselves are also not poisonous if consumed, as evidenced by the many predators eager to chow down on them. Brave gourmands can easily find recipes online on how to cook up their own cicadas for a high-protein snack. Household pets may chase and pounce on these actively buzzing bugs, and may even try to eat them. While full of nutrients, cicadas do have a tough outer shell with sharp edges, which is difficult to digest and may cause problems for cats and dogs. Allowing pests to swallow them whole is discouraged. 

Much attention has been paid to the volume of the shrieking cicadas. Some species have been reported to reach levels of 90-100 dB, which is on par with a power tool or rock concert. And it’s also true that long term exposure to noise above 85 dB is considered hazardous to hearing. However, these safety limits for environmental and recreational noise were established to prevent hearing loss when exposed to high noise levels over 8-hour days, during 40-hour weeks, throughout a 40-year working career. Even though cicadas are extolled as the loudest insects in the world, periodic short-term exposure to their tree-top choruses outdoors will be unlikely to cause people hearing loss from a distance. Rather, enjoy their exuberant and fleeting song of summertime romance.

Ecological Impact

Although appearing infrequently, the abundance of periodical cicadas can have significant and wide-ranging impacts on the local ecology for several years. When cicadas emerge to become a plentiful food source for many predator species, it means other insects that are around every year can potentially survive and reproduce in greater numbers, since fewer of their population are eaten. If these species are pests of a particular plant or crop, then the next season could be a bad one for farmers or gardeners. However, the abundance of food this year also means that predator species can eat well and raise more babies, resulting in a larger predator population the following year. These abundant predators can again focus on the other prey available when cicadas are absent, resulting in a bad year for those pest/prey species. And then, again, the following year, with reduced prey numbers, the predator species population will begin to shrink. Nature will continue to adjust until the next emergence of Brood XIX in 2037. Parts of eastern Arkansas will also see Brood XXIII appear in 2028.

The periodical cicadas emerging now will reach their peak in May, and taper off again by the end of June. But don’t worry, every summer in Arkansas will feature the serenades of numerous other species known as annual cicadas and dog-day cicadas.

Pest Status

Cicadas are not necessarily considered a pest species. As native organisms their regular cycles are an established part of the native ecology, with abundant natural enemies to help keep their populations in check. Although the nymphal stages do feed on tree roots, they do so slowly, and the volume of nutrients they extract at one time is minimal, even with a large population. As noted, the adults rarely feed at all, but females can injure tree tissue during oviposition. Each slit is small, but over time, any physical injury has the potential to weaken tree branches, especially with a large number of cicadas ovipositing at once. These branches could wilt or break off, or become entry sites for canker or other infection. 

Periodical cicadas prefer species of oak, maple, hawthorn redbud, and a variety of fruit trees. They prefer to lay eggs on branches that are 0.25-0.5” in diameter, and thus tend to favor young trees that have the right sized limbs. Older established trees are less prone to damage and are able to withstand minor injuries from cicadas. Valuable newly planted landscape trees and economically important specimens such as orchard fruits may be more susceptible. 

Nurseries and orchards may wish to protect valuable tree stock with mesh netting during the height of cicada emergence, but chemical control is not recommended as effective in most cases, dues to the sheer area of application that would be required, and the difficulty of thorough coverage. Smal individual trees could be judiciously pruned if damage is observed. Susceptible trees should also be kept in good general health with proper mulching and water to keep them robust enough to weather the impending cicadapocalypse.