There are lots of natural wonders in the Midwest. Most of them are annual events, or semiannual like the sandhill crane migration. A few are infrequent or rare. One of the most spectacular events is strangely both rare and regular in occurrence. I am referring to the emergence of periodical cicadas. Although sometimes called locusts, they are not. Locusts are short-horned grasshoppers and belong to a completely different order, the Orthoptera which have chewing mouthparts and huge hind legs.
My friend and fellow Indiana Academy of Science (IAS) colleague Dr. Gene Kritsky, professor and dean at Mount St. Joseph College, Cincinnati, is a world-class entomologist and authority on periodical cicadas. He literally wrote the book (Periodical Cicadas: The Plague and the Puzzle) published by the IAS in 2004. I was honored to be the editor and publishing director.
So how do the periodic cicadas differ from the ones we see and hear every year in mid to late summer? The annual, or dog-day cicadas, are larger with green and black bodies, green veined wings and green eyes. The periodic cicadas (Magicicada) are about half the size of their annual relatives. After emerging white, the bodies of the periodic cicada change to black and orange with orange-red wings. Their eyes are a menacing red. And, by compassion, the number of individuals in the periodical emergence is prodigious -- attempting to overwhelm (satiate) predators in order to ensure reproductive success. Gene informs us there are three species and two kinds of periodical cicadas -- 13-year and 17-year. These two groups are reproductively distinguished into different broods which emerge in different years. The emergences we experience in central Indiana are from Broods X and XIV of the 17-year cicadas. Brood X, which has the most extensive population, is set to emerge this year (2021). Some individuals may appear in late April but expect most of them in May -- waiting for the ground temp to reach mid-60s and a subsequent heavy rain. They will be around for several weeks -- their ghostly shells (exuvia) perhaps longer. Note that due to human activity the cicadas are now less common in the northern half of Indiana. One of the many impressive things you will notice is the noise males generate while courting the silent females -- the world's loudest insect. In a dense population the sound can equal the decibel level of a rock concert. By dense we are talking about +300 individuals emerging per square meter over a two-week period. That extrapolates to 1.2 million per acre!
So why am I discussing these large bug-eyed insects in a gardening blog? The answer: for good reason. Once the insects emerge, they have one goal. SEX -- and this is where gardeners' ears should perk up. Once copulation is complete the female will seek out the young branch tissue of woody plants where she will slit open the tender new bark of branches using her ovipositor to insert eggs. The fertilized eggs develop into nymphs which emerge 6-8 weeks later and literally fall to the ground. This next generation of that cicada brood immediately burrow into the soil about one-foot deep where they attach to plant roots and slowly develop before emerging on schedule, years later. Many of these branch tips will die, turn brown and break off at the point of insertion. Some oviposited branches do not die or detach. For these the oviposition slit will produce a defacing football shaped scar which is obvious for several years. The adult cicadas also have a formidable looking piercing-sucking mouth part, as do all Homoptera (true bugs -- the order which cicadas belong), but the cicada's version is harmless to animals. Gene informed me that while the adults do need to feed on plant juices to stay hydrated, the previously mentioned stem damage is from the slit produced during oviposition. The average number of eggs per female is about 500. That is a lot of ovipositing. The cicadas have been documented to utilize over 200 species of woody plants for ovipositing but are particularly fond of oaks, fruit trees and maples. Given the stress oriental maples experienced from the atypical late spring (Mother's Day) freeze in 2020, these species and specimens may be in special jeopardy. One should also be careful with nursery stock. If necessary, I intend to attempt protecting some of my plants with a leaf blower.
For more facts and super interesting natural history about these curious creatures get a copy of Gene's book (see books & publications indianaacademyofscience.org). Additionally, Gene produced, and Mount St. Joseph released a free app called Cicada Safari -- used for crowd sourcing data on cicada emergence. I recommend you consider assisting in the data collection. It should be fun, while being useful and appreciated. Let your friends know. There is also a great OLOGIES podcast (Mar 1, 2021) featuring Gene and periodical cicadas.
NOTE: While some plant damage will occur, I consider this spectacular phenomenon a rare privilege rather than a plague. Moreover, since I will turn 69 in the midst of this emergence, I am somewhat melancholy knowing it is likely my last chance to experience Brood X of this magnificent creature.
PS: Some of the measures people employed to protect their small trees and shrubs were extreme -- likely causing more harm than good. When I asked, the individuals told me they did so based on advice from Purdue extension agents. To which I responded, that is unfortunate.