Periodical cicada impact on trees


By BJ Price - Preble SWCD



Faithful readers will recall a previous article that covered periodical cicada development and emergence. By now, many of you have witnessed the “turrets” or little mud castles on the ground surface that the periodical cicada nymphs have constructed. If you have not seen the mud castles, look in the woods or near yard trees in places that haven’t been disturbed since 2004. Cicada populations can be very localized and they’ll be much denser in some places than in others.

After they emerge and become adults, which is usually around Mother’s Day, periodical cicadas can be identified by their red eyes and they will live for two to four weeks. After the adult’s exoskeleton fully hardens, they take flight and soon begin to mate and reproduce. Adults will feed very little, and what feeding they do consists of sucking sap from tender branches.

Only the male cicadas sing, which they do to attract females. They do this by vibrating membranes called tymbals which are on the side of their abdomen behind their wings. Multiply this singing by thousands of cicadas and the sound can reach 100 decibels, the same amount of noise as you might hear from a chainsaw at three feet away. The males often synchronize their chorus, creating something of a droning sound. This sound is also thought to deter predators.

After the males and females mate, the female uses her sharp ovipositor to slit the bark of twigs and insert the eggs into the whitewood underneath the bark. This results in the slits or furrows we see in the bark. Often, the end of the twig will wither and die, a condition known as ‘flagging.’ But fear not, for if a twig dies and falls to the ground, it puts the eggs and the soon-to-hatch cicada nymphs that much closer to the soil, where the nymphs will call home for next 16+ years. When the branches where the eggs were laid do not break off, the nymphs simply drop to the ground to burrow in and wait it out until the cycle starts all over again 17 years later.

One should keep in mind that cicadas are not out to massacre your trees. Since the egg-laying occurs on the branch tips, it can amount to a natural form of pruning that causes tree canopies to fill out. We know all about the benefits of earthworm tunnels, and some of you probably do some sort of mechanical aeration on your lawn. Just think how much soil aeration is accomplished by the thousands of cicada tunnels going down into the soil. And they’re doing it all for free.

How can the home gardener prepare for cicadas coming to town? Covering trees with netting is often not warranted unless you have fruit trees or specimen trees near established populations of periodical cicadas. When protecting small trees, use nylon netting with an opening of one-half inch or smaller. Keep in mind, netting can distort small branches and potentially cause more harm than good. If you didn’t see high numbers of them in 2004, or if your home has been built since then, you may not see huge numbers of them in your yard.

As for the effects of flagging on large trees, they “may look a little wonky this year, but next year they will be fine,” according to the Ohio Department of Natural Resources Urban Forester Wendi VanBuren. She notes that cicada damage “really has no long-term effects on healthy trees.” Cicadas depend on trees for their survival, and it wouldn’t make any sense for them to kill the trees that could be prime mating and egg-laying sites for their offspring in another 17 years.

As a rule, insecticides are not effective against cicadas. Many insecticides will kill beneficial insects and you may wind up doing more harm than good. And besides, cicadas feed by sucking and do not consume insecticides applied to leaves and branches. Lastly, they are large-bodied insects requiring high doses to be lethal.

In regards to cicadas attacking you, I lean on the words of the always-insightful Joe Boggs. “Although cicada females have long sucking mouthparts, they will not plant their proboscis into the arms of horrified gardeners. Likewise, they will not use their long, sharp, wicked-looking ovipositors to ‘sting.’ People aren’t at risk unless they look like an oak tree.”

Keep an eye on your cats and dogs. They may walk outside and think a cicada smorgasbord has come to town. If they gorge themselves on cicadas, it may lead to vomiting or constipation, and who wants that for little Socks or Rover?

In short, the periodical cicadas are on their way, they are going to make a racket, they will reproduce, and 17 years later it will happen all over again. Your trees will likely recover from it and in a few years the only thing you might notice will be some scars on the bottom of smaller tree branches. Though we are not bug experts by any stretch of the imagination, the Preble Soil and Water Conservation District is available to answer any of your natural resources-related questions. You can reach the office five days a week at 937-456-5159. Thanks to Jennifer Andon, Joe Boggs, David Shetlar, and Wendi VanBuren for the information contained in this article.

By BJ Price

Preble SWCD