The Virginia Department of Forestry says the periodical cicada outbreak known as Brood II resulted in widespread damage to oaks and other trees across the commonwealth.
"After mating, periodical cicada females lay eggs in the thin-barked outer branches of many different trees and shrubs by slicing into the plant tissue with a sharp organ called an ovipositor, which is also used to lay eggs," Dr. Chris Asaro, VDOF forest health specialist, said in a release. "Within each sliced area, known as an egg nest, they deposit up to 20 eggs."
Asaro said that a single female can create about 30 egg nests, laying as many as 600 eggs.
"When you consider how many millions of female cicadas were laying eggs over the past few weeks, there are literally billions of slices in the trees," he said. "All of these cuts along the length of the outer branches can cause enough structural damage to kill the terminal, which turns brown, a phenomenon known as 'flagging' or 'twig dieback.' "
In areas with very heavy cicada emergence, heavy flagging may be apparent, particularly on oaks and trees overhanging fields and roads. This flagging is visible to varying degrees across much of Virginia's Piedmont and Coastal Plain.
Nevertheless, the VDOF said, most medium- to large-sized trees will not suffer any serious, long-term damage.
"Although it may be hard for some to believe now, most trees will shed the damaged twigs and replace the lost foliage, appearing normal within a month or two," Asaro said. "On the other hand, fruit trees and recently planted or nursery-sized trees may suffer significant impacts from cicadas. Smaller trees generally have thin bark across much of their branch surface, so a much larger proportion of the tree is suitable for egg laying and damage by cicadas. In some extreme cases, small trees may experience enough damage that the entire top is killed back, although many hardwood trees have well-developed root systems and can re-sprout new tops."
The good news — for many Virginians, anyway — is that this won't happen again for another 17 years.
"I say most Virginians, but not all, because there are other periodical cicada broods that emerge in different years and overlap parts of Virginia," Asaro said. "For example, Brood X, which is the largest in geographic extent, overlaps Northern Virginia and parts of Southwest Virginia and is due to come out in 2021. Other broods that impact smaller parts of the state are Brood XIV, due in 2025, and Brood XIX, which is on a 13-year cycle. Since this brood emerged in parts of Eastern Virginia in 2011, it is due to return in 2024."
For more information or to see brood maps and dates for a particular area, go to www.magicicada.org.