After a 17-year, underground incubation period, the Cicadas are coming. The somewhat large, noisy insects will return this summer and swarm in huge numbers in portions of Washtenaw County. WEMU's David Fair checked in with Washtenaw County Conservation District community forester Summer Roberts about the 2021 irruption. There is some good they do for the environment, and there are ways to help mitigate the potential harm they bring to small trees and shrubs.
- This summer will be a lot noisier than usual. 17-year Brood X (ten) cicadas are expected to emerge in the billions in every part of the WEMU listening area. The last irruption was in 2004.
- Periodical cicadas are thought to have evolved the 17-year pattern to avoid predation. They are eaten by nearly anything that can fit them in their mouths, so the survival strategy is to win by sheer numbers. The event will last about two months, beginning in May when the soil warms to 64°F. The nymphs crawl up the trunk of the tree where they molt into the adult form.
- The large insects are not dangerous to humans or animals, but they can kill diminutive trees and shrubbery by damaging the small branches when laying eggs. Larger established trees should survive, even if they appear damaged this summer. It is possible to protect vulnerable plants by wrapping them in mesh or other methods.
- Overall, cicadas may be good for forests, which may experience a growth spurt the year after an emergence, notes University of Michigan professor emeritus Thomas Moore. “The emergence holes allow sunlight, air, water and nutrients to penetrate more rapidly and to greater depths into the soil than typically.” Indeed, the very presence of cicadas is a sign of a robust forest, he added.
- Summer Roberts, Community Forester for the Washtenaw County Conservation District, says the county is still hosting a tree and shrub sale this year, and they can offer advice on protection. Ann Arbor is giving away 10,000 trees as part of their sustainability goal. Tree species offered will be mainly conifers which are less vulnerable to cicada damage.
FAQs about Periodical Cicadas
Due to an influx of concern regarding the upcoming emergence of the 17-year Brood X cicadas, expert tips, handy tricks, and online resources have been compiled to assist you in determining whether additional protection for your trees and shrubs is warranted as well as answering some FAQs.
What are cicadas and what do they do? Cicadas are insects in the order Hemiptera, or true bugs. The nymphs (i.e. immature cicadas) emerge from the ground when the soil temperature is 64 °F. They proceed to climb up bushes and trees where they then molt into winged and wedge-shaped adults with large eyes. The males are pretty noisy - you’ve likely heard them calling for mates. After breeding, female cicadas will cut open slender branches and lay their eggs inside. Once the eggs hatch, the nymphs will fall to the ground, bury down, and live there until their next showing.
Are cicadas dangerous? They are not dangerous to human health or animals. However, some animals, such as dogs may be tempted to eat the insects and may experience upset stomach or vomiting.
Why is this cicada emergence significant? Periodical cicadas have either a 13- or 17- year life cycle which is controlled by their internal molecular clocks. Scientists hypothesize that a timed emergence helps to overwhelm predators and ensures plenty of offspring survive until the next surfacing. However, while this is a good population level survival strategy, such large numbers of cicadas can damage and potentially kill small trees and shrubs as well as recent transplants. Large, mature, otherwise healthy trees may experience some twig dieback (cicadas often target already weak or diseased branches), but generally are able to withstand cicada damage with only short-term aesthetic repercussions.
Why is the Conservation District having a tree and shrub sale during a 17-year cicada emergence? The annual tree and shrub sale accounts for a significant portion of WCCD’s revenue and furthers the organization’s goals to encourage county residents to protect, maintain, and improve our natural resources. New transplants as well as young trees and shrubs can be protected from cicadas.
Whether and How to Protect Your Trees and Shrubs
1) Determine your vulnerability
A. Do you have vulnerable plants on your property?
Cicadas prefer deciduous trees with branches around 3/16" to 1/2" in diameter. Small trees and shrubs with a preponderance of these size branches or new transplants are susceptible to significant damage and possibly death from cicada egg laying activities. Mature, otherwise healthy trees may display peripheral twig dieback, but should be only aesthetically impacted. Bob Bricault, MSUE Consumer Horticultural Educator, Semi-retired (i.e. working part-time) likened the impact of cicadas on mature trees to a bad haircut; it may not look attractive in the moment, but it is a short-term and insignificant impact.
B. What is your proximity to emergence hot spots?
Several sources mention Cherry Hill Nature Preserve and other nearby natural areas, located just northeast of Ann Arbor near Dominos Farms, as being a significant emergence area, but cicadas don’t travel far from their emergence sites. Mr. Bricault observed the emergence first hand in 2004 and thoughtfully reminds us that cicadas live and thrive where soil hasn’t been disturbed by compaction or chemicals, hence, you’re unlikely to see significant numbers of them in urban, suburban, or heavily farmed areas. Gary Parsons, MSU entomologist and Director of the MSU Bughouse, wisely advises anyone new to an area since 2004, the last cicada emergence, speak with their neighbors who might recall the previous emergence. “If they were seeing lots of cicadas back then, they will likely see lots this time too. If they only remember seeing/hearing a few cicadas they will likely be scarce again in that area,” explains Mr. Parsons. This kind of localized knowledge may help you better determine the resources you want to spend protecting your vulnerable trees and shrubs. Even if you are located near a popular emergence spot, you may find solace in the fact that a seasoned manager at the University of Michigan Matthaei Botanical Gardens recalled no significant plant damage in the garden areas or the general landscape during the 2004 emergence.
2) Determine your risk comfort level
Preventative measures take additional time, effort, and money, so you will need to make a personal decision about how much risk is acceptable. You may decide that given your location and past anecdotal evidence of cicada damage, certain trees and shrubs, due to cost, size, or sentimentality, merit protective measures.
3) Gather appropriate supplies
These items can be found for sale online or at big box home improvement stores, garden stores and nurseries.
- ¼” netting/mesh (some sources say ½”, but smaller will further reduce risk), such as row cover fabric or mosquito netting that allows for light and air flow
- Zip-ties or twine
- Double-sided sticky tape, stickem covered cardboard wraps, or insect glue traps (Please use these with caution since they will kill cicada larvae, possibly other insects, and could even endanger squirrels or other animals.)
- Ladder, if applicable
4) Timing and deployment of protective materials
Cicadas emerge when the soil temperature reaches 64 °F, usually in late May or early June, often following a rainstorm. Some sources recommend deploying preventative measures when the first cicadas are heard. If you’d like to try to time your deployment to right before the cicada emergence, keep an eye on soil temperatures through the National Weather Service Soil Temperature Map and listen for reports of cicadas emerging south of your location to determine when to deploy your chosen protective measures. Mr. Parsons also recommends that you keep an eye out for the tunnels that nymphs create when they dig up to the surface, “…looking for chimneys/holes would be one way people can sort of time the beginning of the upcoming emergence, as well as see if there are going to be lots of cicadas in their area. Animals can detect these too and you may notice digging around the bases of trees as they try to dig them up.”
If you have chosen to use netting/mesh, make sure to secure the netting around the main trunk (resembling a lollipop wrapper) or base of the bush using twine or a zip tie to prevent cicadas’ access. Step-by-step directions (and a photo) are available on the City of Ann Arbor’s Forestry website.
If you have chosen to use sticky traps around the tree trunk, you will need to use some ingenuity to engineer them for this specific purpose. Do a test application to make sure they do not damage the bark of young trees. You do not need anything with pheromones or lures. The idea is simply to catch cicada nymphs as they emerge from the ground and attempt to climb up your valuable tree. Be sure to check sticky traps at least daily to monitor if they are still performing as intended (especially after a rain event) and change out as cicada nymphs accrue.
If you need to use a ladder, please do so safely! Use a ladder in the presence of someone else and/or with their help. Otherwise, please notify someone about what you are doing and plan to check in with them once you have finished. Some basic ladder safety tips can be found at the American Ladder Institute.
5) Removal of protective materials
Cicadas may remain active for 4 – 6 weeks, but a quieter natural soundscape is your best indication that the emergence and breeding period has ended, and all protective material can be removed.
Additional Recommended Resources
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