The 17-Year Cicadas and Your Plants

May 18th, 2021

   If you live in an urban setting or other more-populated/less-tree’d area, you may be wondering what all the hubbub is over Brood X cicadas, that bug that emerges en masse only once every 17 years.

Check out the bulging eyes on these 17-year cicadas.
Credit: Marcus Schneck

   It’s entirely possible you may not see (or hear) a one.

   However, if you’re in an area where this family of cicadas laid eggs 17 years ago, you might be wondering if this spells the end of your landscape as you know it.

   The short answer is no.

   Although these bugs seem threatening and foreboding in their incredible numbers and screeching choruses, they do surprisingly little plant damage.

   They don’t bite, they don’t sting, they don’t spread disease, and they don’t even eat leaves or fruits. That ranks them fairly low on the scale of insect mayhem.

   “If you’re freaked out by bugs in general, you’ll really get freaked out by these,” says Dr. Jared Ali, a professor of entomology at Penn State University. “But cicadas look worse than they really are.”

   Ali says the main landscape threat is from the bug’s egg-laying habit.

   After mating, female cicadas use tiny saw-like appendages on their abdomens to cut slits in young tree branches. There they lay little white eggs in rows of 24 to 28 eggs, up to as many as 600 eggs total.

   This cutting can cause branch tips to wilt or die from the egg-laying point outward, a condition known as “flagging.”

   “The only trees to worry about are smaller ones, ones with quarter-inch to half-inch branches,” Ali says.

   Cicadas lay eggs in about 80 different species of woody plants, including fruit trees, nut trees, oaks, maples, dogwoods, and hawthorns.

Cicadas’ egg-laying causes this kind of small-branch damage.
Credit: John Ghent/Bugwood.org

   They have no interest in laying eggs in needled evergreens, and they also don’t lay eggs on or otherwise injure flowers or vegetables, although you may see them resting on those plants.

   Larger trees, Ali says, can withstand slitting damage and probably aren’t going to show any significant damage.

   To protect young or newly transplanted trees, wrap them in netting (with smaller than half-inch openings) or light-weight fabric row covers (usually used to drape over vegetables in the garden). Be sure to fasten the covering to the trunk so cicadas can’t get in from underneath.

   If that’s not possible or if you decide to do nothing, most trees will recover even if some flagging damage occurs. Just prune off the dead ends, and new buds should eventually emerge from the remaining inner branch wood.

Cicadas can cause this kind of branch tip damage, called “flagging.”
Credit: Jim Occi/Bugwood.org

   If you’re about ready to plant a new tree, another option is to wait until summer or early fall – after the cicadas have retreated back into the ground until 2038.

   Ali advises against spraying.

   “You’ll probably do more harm to yourself or to butterflies, bees, and other beneficial insects,” he says. “Besides, these are just going to fly around, do their thing, and die off in a few weeks.”

   Cicada nymphs do feed on tree roots while they’re underground, but Ali says that causes negligible damage and is not worth treating either.

   “If it were that harmful, all of the trees around us would be dead,” he says.

   However, if you’re concerned about that, prune off the egg-laden branch sections and destroy them before nymphs hatch and burrow in.

   Of course, this is all assuming the cicadas find your yard in the first place.

   Cicada populations are largest near wooded areas and in areas with ample trees and shrubs that have been undisturbed for the last 17 years.

   Cicadas don’t favor concrete-laden cities or housing developments in which the land was bulldozed, graded, and replanted from scratch in the last 17 years. Grading uproots the ground-dwelling cicada nymphs and interrupts their food source, which is primarily tree roots.

   Cicadas look a bit like and are often confused with locusts.

   They’re hard-shelled and about the size of a pinky tip, but a key distinguishing feature is their orangish-red bulging eyes.

   That look and cicadas’ incessant screeching noise adds up to what Ali calls a “fear factor” that gives them their worst-than-deserved reputation.

   The cicadas we’ll see from about mid-May through the end of June come from eggs laid the last time that Brood X – the mother of all cicada broods – hatched in 2004.

   This particular brood inhabits most of central and eastern Pennsylvania as well as eastern states running from New York down to Georgia and as far west as Mississippi.

   After 17 years underground, these cicadas emerge into the daylight through inch-wide holes. Soon after, they shed their skins, which you may see on the ground or attached to the bottom of tree trunks.

   Cicada adults at first are soft and white, but their exoskeleton soon hardens and darkens. That’s when the males latch onto a surface (often a tree trunk) and begin making that loud, whirring, screeching noise, which is actually a mating call.

   June is when it gets really noisy.

   Mating time also is when a lot of adults are flying around, often bumping into people and objects since they don’t see well and are rather clumsy.

   This whole scenario takes place over four to six weeks. Then the adults die, the newly hatched nymphs burrow into the ground, and nature’s white noise returns to the more subdued sound of crickets, bird-chirping, and lesser-populated annual “dog-day” cicadas.

   On the plus side, cicadas do have one important redeeming quality… they’re an excellent food source.

   Not only do birds, rodents, and even cats and dogs find cicadas to be a tasty snack, their rotting bodies decay into nutrients and organic matter that feeds soil microbes.

   The next time we’ll see Brood X is 2038.