Temperatures in southwestern Pennsylvania will climb into the high 60s and low 70s this week, signaling that it won’t be long before the region is buzzing under the emergence of hordes of 17-year cicadas.
Only after several days of warm temperatures, and the corresponding warming of the soil, will the big, loud insects begin scratching their way to the surface. That is expected to happen in the next few weeks.
Millions upon millions of the insect will show up in Allegheny, Armstrong, Beaver, Butler, Clarion, Indiana, Lawrence, Venango, Washington and Westmoreland counties, and in southeastern Ohio and the northern panhandle of West Virginia.
Although numbers and range of the insects have decreased in recent emergences, estimates place the number of cicadas at 1.5 million per acre.
The cicadas this year are Brood VIII, which means the rest of Pennsylvania, most of Pennsylvania, will wait not experience an emergence.
The next emergence for most of Pennsylvania will occur in May and June in 2021, when Brood X, one of the largest broods, will emerge.
Across North America there are 13 broods of 17-year cicadas and 5 broods of 13-year cicadas, according to Penn State Department of Entomology. Comprising the broods are 3 species of 17-year cicadas and 3 species of 13-year cicadas.
Pennsylvania has only 17-year cicadas. They occur in 8 different broods, or populations.
Cicada nymphs live underground for 17 years, feeding on sap in tree roots. Then, in that 17th year, when soil temperatures hit 64 degrees – sometime in May – they crawl up through a tunnel in the soil and onto some surface, like a tree trunk, and wait there for their wings to develop.
By emerging in such large numbers, periodical cicadas ensure the success of their species by providing their predators, of which there are many, with more food than they can consume. Through such predator satiation, plenty of cicada nymphs in the next generation survive.
Many areas of Pennsylvania will see annual cicadas this summer, but nothing like an emergence of the periodical cicadas, broods of which surface in May through June every 13 or 17 years, depending on the species.
Periodical cicadas are .75-1.25 inches long. They have bright red eyes on a black to bluish black body, red legs and red veins snaking through their translucent wings.
Annual cicadas, which emerge in late June through August, are about 1.75 inches long and generally green to brownish green.
According to North Carolina State University entomologists, there are about 3,400 species of cicada worldwide. Seven of them are periodical cicadas, three with a 17-year lifecycle and four with a 13-year life cycle.
Periodical cicadas often are referred to as 17-year locusts. Early American colonists had never seen periodical cicadas, but they were familiar with the biblical story of locust plagues in Egypt. When they first encountered an emergence, they worried that a plague of locusts had fallen upon them.
The common confusion between cicadas and locusts continues today. However, locust is a term correct only for some species of grasshoppers.
They molt, leaving those familiar exoskeleton shells behind, and fly clumsily about their new home for the next few weeks. Vibrating membranes in their abdomens called tymbals, the males set up a buzzing chorus to attract females for mating.
About 10 days into the emergence, females will begin responding to the song, mate with the males and start laying their eggs in slits they cut into the twigs and branches of nearly 80 different species of deciduous trees and woody shrubs.
Gregory Hoover, senior extension associate in Penn State’s College of Agriculture Sciences, said each mated female will deposit 400-600 eggs. She will use "the blades of a saw-like, egg-laying device" at the end of her abdomen to puncture the bark of a twig and make a pocket in the wood. There she will deposit 24-28 eggs in two rows, and then move forward to cut another pocket, and lay more eggs.
The adults die, or are eaten by a myriad of bird, amphibian and mammal predators, nearly all of them by late June.
The eggs will hatch in six to seven weeks, and then "the white, antlike nymphs work their way out of the slits and drop to the ground where they enter the soil," where they insert their piercing-sucking mouthparts into plant roots and begin drawing plant fluid. They will remain there for 17 years, metamorphosing through about five stages known as instars.
Brood numbering began in 1893 and that year’s emergence was designated Brood I. When Brood XVII (17) emerged in 1909, followed by Brood I again in 1910, the full range of the 17-year cicadas appeared to have been documented. The 13-year broods, which are mostly southern, were designated XVIII (18) through XXX (30).
