What to Make of this Summer’s Dual Cicada Brood Emergence

Parts of the U.S. are experiencing the rare emergence of two broods of cicadas this summer. A 13-year brood (XIX) and a 17-year brood (XIII) are emerging, predominantly in Illinois, Missouri, northern Arkansas and areas of Virginia, Tennessee, North Carolina, South Carolina, Georgia, Alabama and Mississippi. In Illinois, the northern half is experiencing the XIII brood emergence, while the southern half is experiencing the XIX brood emergence. 

PCT’s Brad Harbison caught up with Tawny Simisky, entomologist, UMass Extension's Landscape, Nursery and Urban Forestry Program, for an update on this emergence and the messaging that pest management professionals and landscape professionals can share about these periodical visitors.

© credit | UMass

Brad Harbison: Is this summer’s dual emergence proceeding as expected?
Tawny Simisky: It's a little difficult to answer because obviously the activity is happening right now and we're relying a lot on citizen scientists - the general public - to be reporting on what they're seeing. There are a lot of great tools out there, particularly the free app Cicada Safari (developed by Mount St. Joseph University, Cincinnati), where people can submit photographs and locations of where they're seeing cicadas emerge. I can tell you that, as expected, broods XIII and XIX began emerging in late April and early May of this year. Looking at Cicada Safari, one thing I noticed was cicadas emerging in very large numbers, particularly following rainfall events that have been occurring in the Chicago area. The public has reported massive emergences following storms on Friday, May 24, and Sunday, May 26.

BH: How rare is it to have two large broods emerge in the same year in relatively the same areas?
TS: I'm relying on other scientists for this information, and they report that this is only thought to occur every 221 years, and that the last time these two broods emerged together was in 1803. So, at that time, if you know your history, Thomas Jefferson was President of the United States and Lewis and Clark had just started their exploration of the Louisiana Purchase.

BH: Are there areas of the country where there is an overlap of Brood XIII and Brood XIX emergences and what can people expect to see in these areas?
TS: It’s funny, but I was recently asked the same question by a grandmother in Massachusetts who was trying to get her grandsons excited about periodical cicadas. The greatest likelihood of overlap between these two broods is in Illinois — in particular, Springfield, Illinois. However, there won't be a broad overlap and it's really difficult to identify which cicadas came from which brood because of the shared timing of their life cycles. 

BH: What is the message that pest control professionals and landscape professionals should share with customers/the general public should they be asked about cicadas?
TS: The main message is that this is not a biblical locust-type event. I think there can be a lot of panic just because they're large, they're very loud, and very noticeable right now. I think it would be helpful if professionals could help reduce that panic and normalize these emergences. This periodical cicada emergence is a phenomenal, entomological and ecological event. I think the messaging is that these insects are native, they've co-evolved with our forests for a very long time and they aren't going to be causing massive mortality of trees. My colleague, Dr. Zoe Getman-Pickering (UMass Amherst), has done some not-yet-published research with colleagues at the University of Maryland and they looked at 16 species of native trees and found that cicada ovipositioning (egg laying by the female periodical cicadas) and the associated flagging that occurs doesn't actually hurt the trees long term. In fact, after about 1-2 years, the trees bounced back and their research showed no negative effect on the size or the health of the trees. And they also had 0% mortality occurring, despite some incredibly dense egg-laying on the trees.

BH: What type of damage can cicadas cause to ornamental trees and shrubs?
TS: Periodical cicadas can cause damage to a wide variety of deciduous trees and shrubs, especially oak trees. This occurs when the females, lay a series of small groups of eggs by inserting them into the twigs. And this can cause small branches or twigs on the trees to be girdled and killed during this process. Historically, there's been some concern that this might predispose the impacted branches to either breakage or easy access, and entry by certain pathogens. However, the overall injury caused by cicadas, including by the nymphs that feed on the roots of the trees that extract fluids from the root (adults also feed a little bit on the fluids from twigs) that that's considered to be relatively very minor. So again, the messaging to any homeowners or property managers concerned about what these insects are doing is that it is an event that's long established in our forests and in our landscapes. And overall, as the years passed, the damage that they're causing is relatively minor.

BH: Can anything be done proactively to protect ornamental trees and shrubs?
TS: The biggest consideration is with new, smaller plantings. As we know, planting young trees is a process that has potential pitfalls, and we want try to protect them from insect pest damage or from disease. So, you make sure that they're planted the right way and that plantings are a good choice for a particular site. In areas that are having cicada emergences in 2024, if netting had been put on these plantings prior to the emergence that would help. Using mesh netting that has no larger than a half inch opening is a good way to protect smaller trees during an emergence year. So, for us in Massachusetts (where brood XIV will emerge in 2025), I think it’s probably a tall order to ask folks to avoid transplanting new trees in the fall in the spring prior…but maybe it's something for us to consider in those parts of eastern Massachusetts, particularly with young oak trees.

BH: Will cicadas impact pest pressure? Do they compete with other insects for food sources?
TS: I would assume that there is some competition, particularly on oak trees. I think that really the competition that occurs mostly with periodical cicadas is their natural enemies. Birds, like grackles and crows, will feed on them. It’s been documented that some bird species even experienced significant fluctuation, or increases, in their population during and after periodical cicada emergences. Even fish eat periodical cicadas that emerge near streams or aquatic environments. Ultimately, the strategy of cicadas is to emerge all at once and in large numbers in order to avoid predation.

BH: As an entomologist, what fascinates you about cicadas?  
TS: I think the coolest thing about cicadas and their life strategy is just that it's a great reminder of how persistent and successful life on planet Earth really is. It's just unbelievable that these insects, after hatching, the nymphs spend 17 or 13 years underground feeding on roots, before eventually emerging and transforming into adults. They do this at the same time and find each other and mate and continue to lay their eggs. We know this strategy has been very effective for a very long time - way before humans started observing them - and certainly before they recorded these observances. The first recorded observance of periodical cicadas was in 1634 by European settlers. However, we know that they were known to the native peoples of the U.S. for centuries prior to European contact. And it's just a great reminder of how life will prevail.