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.
Tree impacts
Female cicadas deposit eggs in tree branches/trunks between 3/16 inch and ½ inch in diameter and create a slit, which can be beneficial for larger and established trees. In addition, the cicadas prune weak or diseased branches, which is called flagging.
Unfortunately, this can be fatal for smaller saplings as the tree is effectively girdled, meaning the branch/trunk is split open.
How to protect smaller, younger trees
Covering vulnerable or smaller trees with mesh/netting is the best defense against the cicadas. Insecticides should not be used as they are ineffective and will harm the other creatures and the environment. For netting, use:
- ¼ inch or smaller gaps to prevent cicadas from crawling through
- be secured to the trunk because cicadas crawl up from the ground, referred to as the “Lollipop method"
Common coverings to consider:
- Agricultural netting (row)
- Cheesecloth
- Polyamide
- Polypropylene
Materials can be found at big box home improvement stores, chain garden stores, and local garden stores, greenhouses, and nurseries in Ann Arbor. Here is a step-by-step guide to wrapping trees to protect against cicada damage:
Wrap the open end of a 2- or 3-foot wide roll of spunbonded, polyolefin fabric around the trunk of the young tree two or three times just under the lowest branches when you see or hear the first cicadas emerge. You also can use 1/4-inch insect netting in place of polyolefin.
Position a zip tie over the fabric or netting and around the trunk, and secure it. Have someone hold the roll while you secure the fabric with the zip tie.
Wrap the fabric around the tree, from bottom to top, overlapping each layer by half. Wrap the fabric snugly, but not so tight it bends the branches. Stand on a tripod orchard ladder to reach the top of the tree if you must. You might need someone to hold the roll for you while you move the ladder.
Clip the fabric to the tip of the top of the tree with a clothespin to hold it in place. Cut the fabric from the roll with scissors.
Staple the fabric together where it overlaps every 1/4 inch or so. Cicadas can fit through spaces 1/2 inch wide or more, so staple closely. Remove the clothespin from the top of the tree after you finish stapling.
Examine the tree for any gaps in the layers of fabric the cicadas could fit through and staple them together as needed.
Do not use insecticides
- There are so many cicadas that will replace the ones killed
- Pets could become poisoned from eating treated cicadas
- Collateral damage —other insects like honey bees and butterflies could be killed
Other resources
