First, to dispel the fears over the much reported double brood emergence, rest assured that in the St. Louis region we will see only a single brood—the 13-year periodical cicadas—says Tad Yankoski, senior entomologist with the Sophia M. Sachs Butterfly House. That said, this single brood will bring about approximately one to one-and-a-half million cicadas per acre (that’s about 40-60 billion cicadas in St. Louis City alone).
“They usually come out around mid-May,” Yankoski says, adding that the ground needs to hit approximately 64 degrees one foot below the surface to trigger the process. “If it’s a warmer spring with a lot of warm rain that saturates the ground, it will be faster. If it’s a late spring with a late frost or it’s chillier, that could delay it.”
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While cicadas are extremely noisy and may bump into you while flying about, the insects are not harmful to humans or animals (even if ingested). They also should have little to no effect on flowers or other non-woody garden plants, says Daria McKelvey, supervisor of the Kemper Center for Home Gardening at Missouri Botanical Garden.
“The biggest concern is the trees and shrubs that are relatively young. The female cicada oviposits her eggs into stems that are about the diameter of a pencil. She will slice into the branch and lay 10-20 eggs, then move further down and repeat the process,” McKelvey explains.
“It cuts into the vascular system of the plant, which can cause the stem to die from where she first starts laying eggs to the end. Mature, well-established trees will be fine. Because they have a large canopy and are well-established, they can compensate for a little damage though you may see some branch dieback.”
For smaller, newer trees and shrubs without much leaf coverage and that aren’t well established, it can do a lot of damage.”
McKelvey recommends waiting to plant any new, young trees and shrubs until after the cicadas are finished emerging. To protect young ones that are already in the ground, she says, “you can put a type of mesh screen around them. It has to be a quarter inch or less so they cannot get through them, but also permeable to water and light.” Passiglia Nursery recommends using fine mesh bug netting. Drap the netting over trees/shrubs and secure it at the base with stakes or weights. Doing so will ensure that the bottom is secured to the trunk, which will prevent cicadas from crawling underneath it.
As for backyard swimming pools, the best course of action is to remove the dead cicadas as often as possible as you would any other organic matter. This can be easily accomplished using a skimmer or other netting.
