The City forestry department has put together information about the 17-Year Cicada emergence that will happen in May/June of 2021, including information on protecting young small trees.
From the City's website:
Ann Arbor, along with large parts of the midwest and eastern United States, will experience a 17-year Cicada emergence in May and June of 2021.
Cicadas do not bite and are harmless to humans and property — other than being a nuisance. They may amass in vast numbers in parks, wooded areas, neighborhoods and can seemingly be everywhere. When they are this abundant, they fly, land and crawl everywhere, including occasionally landing on humans.
Cicada life history
17-year cicadas are also called periodical cicadas, which is a group that includes 13-year cicadas. Cicada nymphs live underground for 17 years and emerge near the end of their life cycle. At this point, they:
molt on trees, live for several weeks and mate
female cicadas lay eggs in small tree branches and trunks
adult cicadas die, new cicadas hatch and burrow into the ground for another 17 years
This batch only emerges when soil is 64 degrees at about 8 inches of depth, which in Ann Arbor occurs in late May or early June