Upload a tree or branch with flagging to iNaturalist, add it to the Magicicada Flagging Project, and when it asks you if the observation has “Magicicada Flagging” select “yes”.
When Magicicada cicadas lay eggs in the branches of trees (ovipositing) branches may become damaged or die which causes the leaves to turn brown. This is called flagging. Magicicadas, depending on their location, oviposit between late April through to the end of June. Flagging will appear in the weeks following ovipositing. Leaves will remain brown throughout the year.
The project works regardless of whether the organism is identified as a type of tree (oak, chestnut, etc.) or a Magicicada cicada. Most people identify trees with flagging as a “Magicicada” but I would not want to take away the option to allow people to identify a tree (oak, chestnut, etc.) over the type of cicada that did the damage.
There is a similar observation field for cicada presence set to flagging/oviposition scars, but it’s not specific to Magicicada and oviposition scars do not always accompany flagging. I do encourage you to use this observation field as well!
When Magicicada cicadas deposit eggs into a tree branch sometimes the branch dies, the leaves turn brown, and the branch droops like a flag. This is called flagging.
Here are some examples of flagging from the Brood X emergence in Princeton, NJ.
Typically flagging is more impactful to trees imported to North America, but it also impacts native species. The positive aspect is it prunes weaker branches, which helps the tree, and helps other plants in the shade of the tree.
Got flagging? Flagging happens when tree branches wilt or die due to cicada egg laying, resulting in bunches of brown leaves. Don’t worry, this will not cause trees to die, unless they are small and weak trees. Flagging can actually do a tree a favor, by removing its weakest branches.
Update (5/4/2024) Here is a link to a video on Twitter/X from the Chicago Botanical Gardens featuring the Garden’s plant healthcare supervisor, Tom Tiddens. He shows us how to net a tree to protect it from cicada egg laying.
As you may have heard, cicadas can damage trees, particularly young or ornamental trees, as they oviposit their eggs in branches. The damage to individual branches is often permanent, and in some cases the entire plant is lost. Native species of trees, like oak and maples, fare much better against cicadas because they have co-evolved for hundreds of centuries. Young trees and weaker non-native ornamentals, imported from outside the United States, fare a lot worse.
Female cicadas use their ovipositor to carve egg nests (egg grooves, punctures, baby cicada cribs) into the bark of tree branches:
Here is an illustration of the egg nests (baby cicada cribs):
Mature trees will receive some damage, but they recover. When branches are damaged they die and their leaves turn brown, which is called flagging:
Do not use pesticides. It isn’t worth it. Bee populations are in bad shape so we don’t want to do any collateral damage to other species. After 28 years of running this web site, I’ve heard a few stories about family pets dying after consuming pesticide covered cicadas or grass. Don’t do it!
Do not surround your trees with a ring of copperhead snakes. By now you have heard that copperhead snakes enjoy eating cicadas at night (although in the photos I’ve seen, they prefer larger species like Megatibicen auletes/grossus.). Gathering a dozen or so copperhead snakes can be time consuming and expensive and they are just as likely to bite you as they are to eat cicadas. Raccoons, bears, coyotes, foxes, and squirrels will also eat cicadas, but I also do not recommend enlisting their assistance. This last one was a joke.
Netting can be effective for keeping cicadas off branches, or on branches, as in the case of this video below where cicada researcher John Cooley had collected many cicadas and wanted to keep them for later. This video is proof that they cannot get through netting:
In my personal experience, which includes two Brood II emergence in my yard, I have seen plenty of flagging, but no death of a tree or shrub. That said, I do not have many small or ornamental trees. I have a 15′ dogwood, azaleas and rhododendrons.
Case study from 2021-2023:
Here’s a small (less than 10 feet) tree that experienced a lot of flagging during Brood X in 2021:
