After 17 years awaiting their big moment, a few million of Washington Grove’s longtime residents will shortly reveal themselves. Our very own periodical cicadas last visited us with gusto in 2004. The reappearance on schedule of what is known as the brood X (pronounced 10) periodicals suggests a certain stability in our local environment. They are not locusts, which are grasshoppers, and they are not the annual dog day cicadas that are active every August. And cicadas are not dangerous: They do not sting, bite, or carry diseases. Neither do they eat our vegetation or gardens. They are, however, annoying, alighting on our clothes, hair, windshields, and especially on our trees. Perhaps you recall their head splitting mating sounds? Well, starting in a couple of weeks and lasting another four weeks, we get to experience it all again.
Peak emergence of cicada nymphs starts around mid-May. During the prior month, nymphs burrow up to the soil surface in preparation for that moment. Right now, they can be found several inches underground. An indication that cicada nymphs are on the move are observations of “something” digging up lawns. Cicadas are good eating for many animals (and some people), and some animals are adept at sensing the cicadas (food) in the soil. These are likely raccoons, skunks, or other soil foraging beasts having a cicada feast. By now, ~1/2” diameter holes have appeared in the ground under trees, leaf litter, and pavers (see photo of a cicada hole taken in Washington Grove on April 17th). Some holes are covered with mud turrets (mounds) while cicada nymphs wait for the soil temperature to reach 64 °F, at which time they will leave the ground with optimal speed. A few hours later, the mature cicada takes flight or climbs the nearest tree. That loud noise we will grow so tired of over the next month? It comes from the males perched in trees, thrumming their hollow abdomens to intensify their love songs.
Periodical cicadas have sucking mouthparts and feed on the xylem fluid of trees (nymphs on roots, adults on tree branches), but this feeding is not known to cause significant damage. However, woody trees and shrubs can be damaged when cicadas oviposit (lay eggs) into branches. Branches preferred by cicadas for oviposition are approximately the diameter of a pencil. The female cicada deposits eggs in slits that she has made in the outer ends of branches. Each slit, referred to as an egg nest, contains 20-30 eggs, and there can be numerous egg nests in a row on a branch. A single female can lay hundreds of eggs. The branch outward from the oviposition wound usually dies back and results in what is known as branch flagging. Because cicadas are so abundant, there is a lot of flagging. Newly hatched nymphs drop to the ground, where they will remain until nature calls in 2038.
What can be done to prevent cicada injury to small, young trees? First, if you had cicadas in 2004 it is likely you will have cicadas and cicada damage in 2021. Some protective measures may be more feasible than others. Although one of the first thoughts may be to treat trees with insecticides, several studies have shown that insecticides are not the best line of defense. Research demonstrated that insecticides applied to sapling Tilia (Lindens) were only about half as effective as mesh nets at preventing egg laying. To be effective, the netting mesh must not be larger than 1 cm (3/8”) in size. Whereas the time taken to enclose a sapling is a few minutes (see instructions at https://www.youtube.com/watch?v=X4vjivdnfMM), insecticide treatments have to be repeated every few days because cicadas are good fliers who will move back into sprayed areas shortly after treatment. More significantly, insecticides used against cicadas are indiscriminate killers of other insects, including pollinators and other beneficials. It may be best to wait until after the infestation, around mid-June, if you are considering planting new trees.
Regardless of their annoying behavior, remember that the appearance of our periodical cicadas is a wonder of nature. They are found nowhere else in the world outside of the eastern United States. Our local brood X is present throughout Maryland and Delaware, and south-central Pennsylvania. Inexplicably, it is also found in western Ohio, nearly all of Indiana, and parts of the southern Appalachian Mountains. When the cicadas appear, they offer wonderful opportunities for observing nature, right here in our own backyards.