While there are over 20,000 insects in northern Illinois, there is one insect that is receiving a tremendous amount of attention this summer. For good reason, it seems everyone is talking about cicadas. Millions of periodical cicadas from two different broods have begun emerging from the soil. This emergence is different because Broods XIII and XIX will emerge simultaneously. Dr. Stephanie Adams, a plant health specialist with the Morton Arboretum, has agreed to answer a few questions regarding the Cicadas.
Dr. Adams, thank you for educating us about this often-misunderstood insect.
Can you please describe the lifecycle of the cicada?
Cicada eggs are laid in twigs of trees or shrubs and then hatch into nymphs, which fall to the ground and burrow into the soil under the tree. For years, the nymphs live underground, feeding on tree roots and sap. They are active and growing, not hibernating. After 17 years (or 13 years for the southern brood), the nymphs of each brood emerge from the soil all at once in mid-May. Each nymph finds a vertical surface, usually a tree, where it molts its exoskeleton and emerges as an adult cicada. The males begin singing to attract females for mating. They can fly short distances to find each other. Once the cicadas mate, about a week or 10 days after they emerge, the female finds an appropriate good twig and uses an organ called an ovipositor to make a slit where she lays about 20 eggs. She may lay up to 600 eggs in a number of twigs. Then all the adult cicadas die. They only live three to four weeks as adults aboveground; they spend more than 99 percent of their lives as nymphs in the soil.
What can residents of McHenry and Kane Counties expect in terms of a cicada emergence?
These northern counties will experience the 17-year cicadas as well as our normal annual cicadas in the fall. Scientists estimate that in a forested area, there can be up to 1.5 million cicadas per acre. The density of cicadas in a neighborhood will depend mainly on how many mature trees there are. It will also depend on whether there has been development or construction since 2007, which would destroy the cicada nymphs and their habitat.
Cicadas are often recognizable by the sound they emit. Why and how do they make such a loud noise?
The sound is the mating call of the male cicada, which they sing to attract females. They make the sound by vibrating drum-like structures on their abdomens to create a loud, high-pitched buzz.
What do adult cicadas drink and eat?
Adult cicadas have piercing-sucking mouthparts. They feed very little. Any feeding is limited to sucking sap from young twigs.
What, if anything, do we need to do to protect our flowers or shrubs from cicadas?
Herbaceous plants, perennial and annual flowers, will not be harmed by the cicadas, they are not preferred hosts or tissues that they feed on or lay their eggs in. Some flowering trees are hosts of periodical cicadas, which are listed below. These can be damaged by egg-laying. The directions on how to protect these trees are also listed below.
Do we need to protect our trees from cicadas?
They do no serious harm to mature, healthy trees. They feed briefly on the sap of woody plants when they first emerge, but not enough to affect a mature plant. The greatest damage they do is when female cicadas cut slits in small twigs and stems of woody shrubs with her ovipositor to create a place to lay their eggs. The twigs affected are ⅛ to ¼ inch in diameter. After the eggs hatch, those twigs may die and break off, but a mature tree can spare some twigs and will soon grow new ones. Very young trees that were planted within the last couple of years as well as older, unhealthy or stressed trees are at risk of significant harm.
Cicadas are not particular and will use many kinds of trees and shrubs as hosts. They are known to lay eggs in oak, maple, hickory, apple, birch, dogwood, linden, willow, elm, ginkgo and pear trees. However, only very young, unhealthy, or stressed trees are at any risk. Cicadas also may lay eggs in some shrubs, such as rose, lilac and forsythia. They tend to avoid conifers such as pine, spruce, and fir. According to Arboretum records, some of the plants most affected 17 years ago were maples, cherries, ashes, hawthorns, willows, mountain ashes, oaks, pears, roses, privets, poplars, serviceberries and beeches.
To protect trees and shrubs, first, make sure all your trees are well-watered and healthy, with no unaddressed disease problems. Healthy trees are always better able to withstand any pests and diseases. For young trees, wrapping their branches in netting will keep cicadas out so they can’t lay eggs in twigs, while allowing air and sunlight to reach the tree. Wrap the tree by early May, before the insects emerge, and keep the netting on for about six weeks, until the insects die.
You can use tulle – the nylon or polyester mesh used to make ballerina tutus – as the protective netting. It is sold in fabric and some hobby stores. Landscape supply companies also sell insect netting. The netting needs to have a fine enough mesh to keep out cicadas, with holes no more than ¼ inch wide. It must also be strong enough to last for several weeks on the tree. Don’t use wide-mesh bird netting with holes ½ inch wide or more; that won’t stop a cicada.
Wrap the entire whole branching area of the tree. It will likely take at least several yards of fabric. Where sheets of fabric meet, overlap the edges, tuck them under once or twice, and secure the roll with binder clips, clothespins or staples. Below the branches, gather the netting around the trunk or the base of the shrub. Tie the fabric so there is no gap more than ¼ inch, but not so tightly that it damages the bark. Netting must stay on the tree for about six weeks, beginning in late April or early May. Be sure to remove the netting and any string or rope tied around the trunk once the cicadas have died.
Do you recommend that our readers use pesticides to kill the cicadas?
The Arboretum does not advise homeowners to use insecticides against cicadas. There are too many cicadas and it would be futile. Insecticides also can harm beneficial insects that control other pests, leading to insect and mite outbreaks unrelated to the cicada emergence. Netting is the best protection for susceptible trees and shrubs.
Are cicadas beneficial to the environment in any way?
Yes, cicadas are beneficial native insects. A cicada emergence is a bonanza for animals. You may see many kinds of animals feeding on them, including squirrels, raccoons, skunks, foxes, coyotes and dozens of bird species. The feeding frenzy can have complicated ripple effects on the local ecosystem. For example, with an ample food supply, more songbird hatchlings survive, so populations of some bird species increase. At the same time, birds that have plenty of cicadas to eat may not bother to hunt caterpillars of other insect species, allowing more of those insects to survive. Meanwhile, once cicadas die, they will decompose into valuable fertilizer. Cicada nymph exoskeletons and adult carcasses will feed soil microbes and provide nutrients such as nitrogen that encourage plant growth. Spread them out so they will decay more quickly. If you put cicadas in your compost, make sure they are mixed with plant matter. Turn and water the compost frequently to encourage decomposition.
Cicadas are used in a variety of recipes from cookies to tacos to miso soup. Have you ever eaten them? How were they?
I have eaten different insects, but I have not tried cicadas, yet.
Kathleen Carr is the owner of The Growing Scene, Inc.,a landscaping company. She can be reached by calling 815-923-7322 or emailing her at Kathleen@thegrowingscene.com. Have a gardening question? Please contact her. She may address it in an upcoming column.
