Cicadas – Take 2, noise & plant damage

Tim Iverson
Naturalist

(5/2021) For the eastern United States the soundtrack of the summer is cicadas. Annual, or sometimes called ‘dog day’ cicadas come and go every year, but this year we are in for a multigenerational event. Brood X, as in the Roman numeral 10, cicadas are set to reemerge after nearly two decades underground.

These periodic cicadas were last seen in 2004. In a time before smartphones and social media, these entomological darlings were midwifed into existence as a result of a long lifecycle process. From New York to Illinois down to Georgia, cicada nymphs will summon themselves up from the soil and ascend to the treetops. Their synchronized exit ensures safety in numbers - their only defense. The nymphs will crawl up to the forest canopy, shed their juvenile shells, then emerge as an adult ready to sire the next generation.

The purpose of their subterranean emergence is not to preserve their own lives, but to create the next generation. By crawling to the surface, the cicadas are now able to find a mate, which they attract through their shrill serenade. What may sound like the cacophony of swarming critters is a unique song that differentiates different species from one another. After cicadas mate, the female will lay the eggs into the stem of a plant or branch of a tree. Once the eggs hatch the larva will drop to the ground and burrow into the soil. Here they will spend the next 17 years growing into maturity by feeding on the sap from plant roots. Once they reach full size the cicada nymphs will dig to the surface, shed their skin, and begin the process all over again.

High in the tops of trees the adult males will begin their siren song beckoning any female within earshot to come and mate. Their songs are loud enough to be heard over significant distances too. The cicada produces these love lullabies in a really unique way. Many insects, like crickets, produce sounds by rubbing together different parts of the body. This is not the case for cicadas. The organ responsible is a ribbed membrane located at the base of the abdomen called a tymbal. These tymbals are contracted inward causing them to buckle and produce sound. Then the cicada relaxes the muscles and the tymbal pops back out and again produces a noise. The sound resonates within the abdomen, which is mostly hollow, to amplify it.

Cicadas perform these contractions very rapidly and will alter their body positions to modify the song. The noise created by them reaches up to 100 decibels, which is as loud as a lawnmower. Congregated en masse, large groups of these can be deafening to the surrounding area and even disorent predators.

Large groups are what cicadas do best. These awakening Brood X cicadas make the largest insect emergence in the world. In densely packed areas they have been found to have as many as 1 million cicadas per acre. This is part of a necessary survival strategy called "predator satiation."

Billions and billions of cicadas show up on scene to the delight of nearly every other living animal. Cicadas don’t fly well. They don’t walk or run well. Cicadas are clumsy and lack good physical coordination. Birds, fish, turtles, snakes, lizards, raccoons and other mammals have never had it so good when it comes to preying on a potential meal. They will dine until they simply cannot eat anymore. By sheer volume the cicadas survive. The other trick to their survival is the 17 year odd-numbered life cycle.

Cicadas often get grouped together or confused with locusts. As an insect people tend to assume the worst, creepy crawlies give people the heebie jeebies. Cicadas are not locusts and are actually more akin to leaf bugs or even aphids. They belong to a family of insects, Hemiptera, which have a piercing mouth used to suck the sap out of plants and trees. Their mouths have a sheath-like encasing that retracts between the legs when not in use. When they are using it the sheath extends and contains four needle type proboscises that pierce into plants. They will use these like a straw to slurp out the sap. Cicadas don’t bite or sting, are not venomous, and pose no threat to people or crops at all.

Cicadas tend to emerge once trees have grown leaves. Deciduous trees such as ash, maple, oak and even red bud are the preferred host trees of periodical cicadas. Young trees especially are at risk. Damage comes from female cicadas piercing the tender outer branches with their ovipositor and inserting eggs. These eggs hatch and feed on sap causing the rest of the branch to brown out to the tip and die. At some point, the nymphs drop to the ground burrowing to remain for the next 17 years.

Cicadas feed only on sap and do not bite or sting. They are not major agricultural pests, but in some outbreak years, the sheer numbers of females laying their eggs in the tender outer branch tips may overwhelm trees and smaller trees may suffer real damage. Some species have turned to crops such as sugarcane and in a few cases have injured cash crops such as date palms, grapes, and citrus trees. Cicadas some-times also cause damage to ornamental shrubs. A simple covering with a screening material like cheesecloth will prevent damage to small trees and shrubs.

Damage from cicadas is caused by their egg laying method. Cicada females have an organ called an ovipositor. This ovipositor is used to pierce twigs about the thickness of a pencil, where she lays a few dozen eggs. Sometimes this action causes the end of that branch to die. On large trees these branch tips stand out against the dark green of the rest of the tree. A good windy thunderstorm will eventually bring these dead branch ends to the ground, ending the cycle of cicada worries. I anticipate this pruning will actually benefit homeowners with large trees who couldn't hire a tree service to do the same thing.

If you live in a neighborhood that is less than 17 years old, you may not see any cicadas. Because they live underground for 17 years, any disturbing of the soil is enough to rid the area of cicada nymphs. Cutting down trees removes the roots the cicadas feed on for this long period of time. If you live on previously farmed ground the cicadas will be rarer on your place. If you live in a neighborhood with few large trees you will have only few of the cicadas this year.

If a cicada does land on you, it is not for some nefarious purpose; it is just that you were in the way. Because they are harmless to people and animals alike there is no reason to be particularly worried if you come into contact with one. As the clumsy swarms flitter about it is not uncommon for cats or dogs to eat them. Their exoskeleton can be a little tough to digest and may cause some gastric distress or an upset stomach, but otherwise pose no threat and pets should be just fine.

People have been known to eat cicadas too. Recipes abound online and they are often described as having a shrimp like flavor. Individuals with shellfish allergies should exercise caution though, as they are in fact related to shrimp.

Because of their periodic 17 year emergence an average person would be able to see this cohort of cicadas about four or five times in their lives. They are a multigenerational event that spans decades. Brood X will emerge sometime in late spring or early summer. Once they are here the swarms will announce their arrival heralding in the legions of insects mating over the course of four to six weeks. After this extravagant show of force they will disappear underground for another 17 year cycle to remerge in 2038.

Read Amanda Markle: Cicadas – Why every 17 years?