As if they hadn't already experienced enough abnormality this year, residents of northern Wilkes and much of Surry, Alleghany and Ashe counties were treated to the surreal invasion of Brood IX of the 17-year periodical cicadas this spring.
In Wilkes, Brood IX appeared in mid-May from Thurmond on the east to Purlear and Parsonsville on the west and as far south as Millers Creek and Hays.
Emerging from the ground like zombie insects and leaving countless half-inch holes, they soon exited their exoskeletons and left these husks behind on tree trunks as they transformed from nymph to as adult stage - about one and a half inches long, with red eyes and orange veins in their wings.
They quickly also made their presence known with a high pitch hum, likened to frogs or crickets on steroids and made by contracting and releasing a portion of the torso called tymbals. The nearly deafening matting call of a swarm of cicadas can reach 85 decibels , or slightly louder than a diesel train.
Unlike the periodical cicadas, the larger dog-day cicadas produce a pleasant late summer sound.
Periodical cicadas in a given area synchronize their emergence, so their sheer numbers swamp the ability of predators to feed on them when adults come out of the soil after feeding on tree roots for most of the previous 13 or 17 years. Birds, squirrels and other predators consume all they can stand, leaving the bulk of the horde to focus on reproduction.
Under ideal conditions, they may emerge at the rate of millions per acre, said Dr. Clyde Sorenson of N.C. State University’s Department of Entomology and Plant Pathology.
Once mated, female cicadas use a saw-like structure called an ovipositor to cut slits in twigs on trees, and deposit their eggs in these cuts. This activity often causes the growth beyond the slit to wilt, or “flag.”
Sorenson said this looks bad for trees, but the damage is transient. The eggs hatch and the cicada nymphs either drop or crawl to the ground, where they burrow until they find a suitable tree root. They settle in for 17 years of sucking on tree roots, gradually deeper, until it is their turn to come up, sing, mate, lay eggs and die.
Sorenson said the feeding activity doesn’t appear to cause significant harm to host trees. “We think cicada nymphs keep track of the passage of time by tracking fluctuations in the nutrients they gather from the trees, and the variation in temperature over the course of the year; other cues may be important, as well,” he said.
Their emergence is triggered by soil temperature — about 64 degrees several inches below the surface.
The periodical cicada is native to North America and exists nowhere else in the world.
Researchers have been tracking the broods for more than 100 years. In the late 1800s, American entomologists created the first good maps of the insects’ ranges. Relying on a form of crowdsourcing, they sent circulars to postmasters in the eastern U.S. each year and recorded their responses.
The Great Eastern Brood of 17-year cicadas will emerge across a wide swath of the eastern U.S. next year, including some parts of western North Carolina.
The Great Southern Brood of the four species of 13-year cicadas will emerge from much of the Piedmont of North Carolina in 2024.