Field Notes: Why We Don’t See Cicadas in the Northwoods
Making national headlines, the 17-year cicadas were making a ruckus throughout eastern parts of the US leaving me to wonder, why don’t we see cicada swarms in the Northwoods of Wisconsin?
Cicadas have a limited and mostly eastern distribution in the United States, reaching as far north as New York state, down to Louisiana and Georgia in the south and barely extending into Kansas and Oklahoma in the west. They hatch on 13- or 17-year cycles and specific cohorts, which are also known as broods, hatch in offset years.
The recent batch of cicadas is part of Brood X, the largest cohort of 17 year cicadas that occurs in the US. There are 12 cohorts of 17-year and 3 cohorts of 13-year cicadas. Brood X began erupting from the ground in mid-May, predominantly in Washington DC, Maryland, Pennsylvania, Indiana, Ohio and Tennessee. The next big hatch will take place in 2024 and will include a brood of 13 year cicadas that will hatch out in the central southern part of the US and a 17 year cohort called Brood XIII that will hatch in southern Wisconsin, northern Illinois and parts of Michigan and Iowa.
The deep frost line and unpredictable frost-free date in Northern Wisconsin may be reasons that temperature conditions are not hospitable for the periodic cicada life cycle.
Cicadas begin to emerge when soil temperatures hit about 64 degrees, which occurs in mid-May throughout most of the cicada range. During emergence, non-flying nymphs crawl out of the ground. Males emerge in higher numbers at first, often bearing the brunt of the heavy predation that occurs during the early emergence period. Females emerge slightly later and, since predators are already satiated, females often face lower levels of predation.
Emerging nymphs shed their juvenile skin and morph into flying adults within an hour of emergence. It takes about five days for the skins of newly emerged males to harden enough that their noise making tymbals can create their deafening song.
Males group together and each species sings a unique and extremely loud chorus to attract females. After mating, females implant their eggs in incisions at the tips of tree branches before dying. Eggs hatch after 6 or more weeks depending on temperature conditions. Hatching juvenile cicada look like tiny white ants and will burrow 8-12 inches down into the soils to begin feeding on sap from grass and shrubs. Juvenile cicadas will burrow deeper over the next 12-13 years as they grow through five different developmental stages. They will also switch to feeding on the sap of tree roots as they grow.
In the early spring of their 16th year, the periodic cicadas will tunnel up to within 6 inches of the forest floor and will hang out for a full year before receiving the necessary temperature cues to tunnel up and join their billions of brethren for a short stint above ground.
Glaciation histories and climate may also be reasons that periodic cicadas are not in Northern Wisconsin. Ice sheets covered much of this region as recently as 20,000 years ago meaning there were no forests or cicadas at that time. As forests have expanded, the unique periodic cicadas have only had approximately 1,100 generations to adapt to the ‘newly’ established forests and temperature conditions of these more northern regions.
For a species whose reproductive success relies on periodic, grouped chorusing behaviors that only last for 2-3 weeks every 17 years, dispersal into northern habitats may not occur anytime soon. Evidence supports that when populations of cicadas on the northern extent of their ranges face fragmented forest habitats, they are more likely to go extinct.
Only time (in intervals of 17 years) will tell if this unique group will ever expand into the forests of Northern Wisconsin.
While things may have quieted down for now, the rain of trillions of juvenile cicada nymphs will begin soon and last throughout August. Each adult female cicada can lay 500 or more eggs. Those juveniles will hatch out from the tips of trees and fall to the ground where they will nestle in until 2038.
It is intriguing to contemplate what those buggy red eyes will witness when they next emerge into our ever-changing world.