Cicada Invasion: Brood X

​Every year, green cicadas pop up in late spring and early summer and start “singing.” Of course, to us, it sounds a whole lot more like screaming! The shed skins of cicadas (which we always thought look a little like cicada ghosts) will litter the sides of houses and trunks of trees. And then, just as suddenly as the screaming started, it’ll stop, and the cicadas will be gone until next spring. 

​But this year, things are going to be a little different, because 2021 marks the return of Brood X.

​The name sounds a bit intimidating, but it’s really just the Roman Numeral for 10. Brood X is the 10th generation of a line of 17-year periodical cicadas.

​What does that mean? To understand, we’ll have to take a look at the life cycle of cicadas.

The Life Cycle of Cicadas

​Adult cicadas vibrate their tymbal organs, which are membranes on both sides of their abdomen, in order to attract other cicadas in the area. This vibration creates the roar we associate with cicada breeding season, and can easily approach 100 decibels. That’s about as much sound as a leaf blower or chain saw!

​Once enough cicadas have gathered together, males will begin courting females with courtship calls. Females express their return interest by an audible flick of their wings, adding even more noise to the chorus.

​After mating, the female cicada will find a small, thin branch or twig to lay her eggs. Using a rigid appendage on her abdomen, the cicada gouges a line into the wood where she then deposits batches of 20 to 30 eggs. The average female can lay around 600 eggs, which means she can do this upwards of 30 times!

​Fertilized eggs will develop in their nests for about 6 to 10 weeks before hatching. You’re probably familiar with the idea that many bug species start their lives out as larvae. Cicadas, on the other hand, have what’s called a gradual metamorphosis. So, instead of larvae, they’re called nymphs. 

​Freshly-emerged cicada nymphs drop to the ground immediately after vacating their eggs, and then burrow into the ground within a few minutes. They’ll settle about a foot or so beneath the surface and attach themselves quickly to a food source. 

​Nymphs usually prefer the small roots of trees, but are also known to attack the roots of grasses and other herbaceous plants as well. Using their sucking mouth, they pierce the root and draw out xylem fluid (water and nutrients transported between plant cells).

​Cicada nymphs will shed their skin a few times underground, and then once more above ground before their exoskeleton hardens and they are officially adults, where they repeat the cycle over again.

What makes Brood X different?

​The cicadas we see annually are green in color, and relatively reasonable in number. You see them around, and they sure make a lot of noise, but they aren’t exactly overwhelming. 

​Brood X, on the other hand, is made up of periodical cicadas. They are brown to black in color, with yellowish wings.

​“Periodical” is used to describe species that go dormant between generations. In the case of cicadas, there are two types: 13-year periodical and 17-year periodical. The nymphs of periodical cicada species hide underground for 13 or 17 years at a time before re-emerging as adults to breed.

​Brood X is the newest generation of 17-year periodical cicadas. The parents of this generation mated and laid their eggs in 2004. In the last 17 years, the nymphs have been feeding and shedding about a foot underground. 

​This May, over a trillion Brood X nymphs are expected to pop out of the ground and shed their skin one final time before spreading their wings and beginning their adult lives.

The Danger to Your Trees

​With trillions of cicadas emerging, at least half of them female, and each female capable of filling over 30 nests… that’s a lot of gouges in a lot of trees. The cuts needed for a cicada to lay her eggs are pretty shallow and not very long, but they can still do some damage. There’s also concern that the open wounds may allow pests a to get a foothold into your tree, or bacteria an entry point to infect. 

​As cicadas prefer to lay their eggs in small, thin branches, they usually pick young twigs near the end of their main branch. Though the injury isn’t that big, it’s more than enough to kill off the twig. 

​Older, well-established trees can handle the death of some twigs just fine. The dead ends usually drop off in the weeks following the cicada laying her eggs. In some cases, the twigs recover, though the location of the nest will probably be structurally weaker than the rest of the branch. 

​Younger and smaller trees, on the other hand, may be in genuine danger from Brood X. Plant nurseries, orchards, strawberry and blueberry farms, and even landscaping trees planted in parking lots and along city streets are all likely to be targeted by this new generation. 

What can you do?

​So how can you protect your trees from the onslaught of egg-laying cicadas? The popular answer is to spray a lot of pesticide. 

​Unfortunately, most pesticides will do nothing to discourage female cicadas from a potential nesting site. Any pesticide strong enough to deter them will likely end up hurting your tree in the process. 

​The tried-and-true solution for protecting young trees from cicadas is mesh barriers. 1.0-centimeter mesh, to be exact. Studies have shown that trees protected with 2.5-cm mesh were just as damaged as trees not protected at all. 

Basically, that means you need pretty tightly-woven mesh to keep cicadas out. If the gaps between threads are more than a single centimeter, the pesky bugs will worm their way in and go about their egg-laying like normal.

Looking for more information? Check out the UGA College of Agricultural and Environmental Sciences article.

---

Author

​​Emily Casuccio is sister and sister-in-law to Rebekah and Scott Rushing, and has over half a decade of experience in copywriting, copyediting, proofreading, and developmental storyboarding. She's worked with both published and undiscovered authors on both fiction and nonfiction, and takes pride in supporting local businesses. Her passion lies in the written word and helping authors of all capacities realize their dreams and achieve their fullest potential. To learn more about her, read samples of her work, or contact her, visit her online portfolio.

Sources:
ABC News
Tree Care Industry Magazine
EcoWatch
Spring-Green
Song of Insects
Bug Guide
​CNet