Music to Their Ears: Periodical cicadas are loud but pose little threat to trees

By on June 28, 2017

This year, western North Carolina got an earful.  A 17-year periodical cicada emergence is coming to an end, but is leaving ringing ears and dead branch tips in its wake.

Approximate estimation of the 2017 periodical cicada emergence; map from cicadamania.com

North Carolinians in the emergence areas no doubt heard the irritating symphony of periodical cicadas as they tried to locate a mate.  That’s right, what sounds like loud, annoying chaos to you is music to cicadas’ ears.  The males are the ones responsible for those long, loud songs and females respond with a clicking sound.  They communicate back and forth, getting closer and closer until finally making contact.  (The female cicadas’ clicking sounds can actually be mimicked by snapping one’s fingers and luring a male cicada in.  Of course, the cicada will be pretty disappointed to realize it’s just a finger.)

After finding one another and mating, females use their egg-laying structure, called an ovipositor, to drill grooves into the tips of tree branches and lay eggs.  This is where they can sometimes damage trees.  This egg-laying method can kill branch tips, a symptom referred to as “flagging” since the dangling brown tips look like hanging flags.  Large trees may be covered with flagging, but usually recover without long-term effects.  While not common, small or weak trees could die from such damage.  Covering susceptible small trees with netting to prevent egg-laying should protect them if needed.  This year, white oak seemed to be hit hardest by the periodical cicadas, but many hardwood trees are at risk, including maple, ash, elm, and other oaks.

Trees with flagging caused by periodical cicadas typically recover from the unsightly damage. Image taken in Caldwell County by Justin Query, NCFS.

Along with their loud noise and minor damage to trees, another nuisance of the periodical cicadas is that they are attracted to loud, vibrating equipment.  Individuals in an outbreak area might have found themselves covered in cicadas if mowing the lawn or operating power tools.  To reduce this, it’s recommended to do these activities earlier in the morning.  Of course, you don’t want to be more annoying to your neighbors than cicadas, so don’t head out to do your yard work too early!

Many people refer to cicadas as “locusts”, a name typically reserved for a grasshopper-like insect.  However, calling cicadas “locusts” has historical roots thought to be derived from the biblical locust plagues, where millions of insects descended upon Egypt.  While this massive cicada emergence isn’t that of the biblical plague, many do scratch their heads and wonder why there are so many of them.  Many insects use different kinds of defense mechanisms to avoid predation: for example, camouflage, mimicry, and defense compounds.  It is thought that periodical cicadas come out in droves in a defensive strategy called predator satiation.  Essentially, there are so many cicadas, predators become full and can’t eat them all.  It’s a survival strategy that calls for a few cicadas to take one for the team and be a bird’s lunch for the greater good of all cicadas.

In short, periodical cicadas are your rude, partying neighbors.  They make a loud ruckus late into the night and might leave a mess in your trees (at least it’s not toilet paper), but keep in mind their annoyance is temporary and they’ll be gone before you know it… for another 17 years at least.

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