ANN ARBOR – Brood X periodical cicadas are about to emerge for the first time in nearly two decades in areas of Southeast Michigan.
The insects, which develop underground for 17 years, crawl out of the ground in May and June and feed from plants and trees and lay eggs in twigs. Harmless to humans, cicadas do not bite, but can do damage to shrubs and young trees.
According to the city of Ann Arbor, those concerned about small or vulnerable trees should cover them with netting or mesh to repel the cicadas. The city also said insecticides should not be used against the bugs.
University of Michigan entomologist Thomas Moore said despite cosmetic damage the bugs can cause, they may be good for forests, which sometimes experience growth spurts in the year following an emergence.
Moore, a professor emeritus in the Department of Ecology and Evolutionary Biology and at the Museum of Zoology, said that the holes created by a cicada emergence allow air, sunlight, water and other nutrients to penetrate the soil more rapidly. He added that the very presence of the bugs is an indicator that a forest is robust.
Tom O’Dell is a natural areas and collections specialist at U-M’s Matthaei Botanical Gardens and Nichols Arboretum. He was in Ann Arbor in May 2004, the last time the 17-year cicadas emerged, and has some advice for homeowners concerned about potential damage to their gardens and yards.
The university released this Q&A with O’Dell:
What was it like in the U-M botanical gardens the last time the Brood X cicadas emerged?
I remember seeing cicadas in a grove of buckeye trees. There were thousands of individuals on the branches and trunks. And though they were concentrated in the buckeyes, they did lay eggs on other tree species in the immediate area such as ash, oak and black cherry.
They did not seem too particular about the species, as long as the tree had some stems in the half-inch-diameter range. They were found on trees of varying ages, but the female cicadas do prefer younger trees. Relatively few individuals were found in our display gardens and landscape areas close to our building, which was about a quarter mile from the emergence epicenter.
How loud were they?
The volume of the brood was loud enough to be heard up to a half mile away. When standing in the middle of the brood, the volume was so loud that two people within a few feet of each other had to raise their voices to converse. I guess I would describe the sound as a continuous droning.
What was the extent of the damage to trees at the botanical gardens after the 2004 cicada emergence?
The most obvious damage was found on trees in and close to the epicenter of the emergence. One could see browning and drooping of branches, but nothing devastating. Since this was in a woodland area, we were not too concerned about the damage. There was also minor damage to the plants in our garden areas, and we did some pruning of what we thought was excessive damage on some of our ornamental plants.
Did any of the trees die, and is the 2004 damage detectable today?
We did not lose any plants to the insect. The damage was largely cosmetic, and there is no visible remnant damage to be seen today.
What advice do you have for homeowners in potentially affected areas such as Ann Arbor?
Young trees could be vulnerable to female cicadas laying eggs in their stems. Until emergence begins, homeowners will not know if they are in an area where large numbers will appear, so it’s difficult to predict the risk of plant damage. It is also a matter of how much damage one finds acceptable. Mature trees will recover just fine.
I think the information put out by the city of Ann Arbor is helpful, and I would recommend that homeowners be prepared to protect their young trees of greatest value.
Will the U-M botanical gardens be taking any special precautions?
We will not be taking any extraordinary measures to protect plants here at the gardens, but we will keep an eye on younger plants that are more vulnerable to incurring excessive levels of damage.
I think that knowing more about the ecology of these insects and their place in the natural world will help reduce anxiety and increase the fascination for the upcoming emergence, and it will also help people decide how they will respond.