Brood X Cicadas, Pt 2

When will we start to see the 17-year cicadas emerging from underground in the Philadelphia region? Academy Entomology Curator Jon Gelhaus tells us what to expect in Part 2 of Brood X Cicadas, and he can’t wait to see and hear the big show. To read Part 1, visit this link.

How many do you estimate will emerge?

If you are in an area with periodical cicadas, you will know it. You will see many of the nymphal exoskeletons attached to trees and other plants in May to June, and you will hear the cicadas singing (chorusing) in the treetops. For the entire Brood X across its wide range from the upper Midwest to D.C. area and from Philly and New York, there will likely be billions of cicadas emerging.

Is it possible some of us won’t see any at all?  

For the Philadelphia region, it is likely you will not see any periodical cicadas. From our records from past emergences of Brood X, documented by the Academy’s insect specimens, historical accounts and observations from 2004, these cicadas have a very spotty distribution in our region. For most of us, we will need to go to a specific place to see them, particularly if you live in Philadelphia and Delaware counties, and adjoining counties of southern New Jersey. If you live to the north and west of the city, you are more likely to hear or see them, but still they are not everywhere. In other areas, such as around Washington D.C., this brood is far more common, even in the city. 

Are they noisy? 

Male cicadas communicate to females through their songs, as it is a way for females to select among males to mate. Females will respond to a male singing by flicking her wings. Males make these songs by rapidly vibrating a drumlike membrane (tymbals) in their abdomen, and the abdomen amplifies the sound. When you have thousands of periodical cicadas in one small area, like in a set of trees, they will sing together, called chorusing. And remember, you can find up to three species of periodical cicadas in one area – each with a distinct song – and all chorusing together. It is a wild symphony, and will continue on warm days for several weeks in an area. 

There is a well-known song Bob Dylan wrote about receiving an honorary degree at Princeton University on June 9, 1970 called “Day of the Locusts” in which he sings “the locusts sang their high whining trill.” He was referring to the emergence of Brood X, and Princeton is one of the known localities for that brood.  As an aside, these cicadas were often called locusts by the first European settlers as they  reminded them of the plague locusts (grasshoppers) mentioned in the Bible.

Closeup of the ovipositor of the female Magicicada, which uses it to drill into a twig and deposit its eggs.

Are periodical cicadas dangerous to me or my pets? How about my garden? 

Relax. Periodical cicadas, like our annual cicadas, are harmless to us and our pets. They don’t sting or bite. In fact, people can eat cicadas (and often do during periodical cicada emergences), and dogs and cats like them also. (My dog George loves to sniff out the emerging annual cicada nymphs).

Female cicadas do lay their eggs inside small tree twigs, and the twig beyond the eggs will usually die back (called flagging). For periodical cicadas, with their large population emergence, this can be noticeable. It is a natural form of twig pruning for established trees and doesn’t do them permanent harm every 17 years. But you might want to be careful with newly planted trees if you are in one of areas with periodical cicadas. It is suggested that you don’t plant young trees this spring, or if you do, net them through June to keep the female cicadas from laying eggs into the stems.

Spraying to kill nymphs or adults is of little value, won’t have an effect, and they aren’t going to harm you – so it is a waste of time, energy and chemicals. Don’t do it. You will just kill other beneficial insects like bees.

When will we start to see these 17year cicadas in the Philly region and for how long? 

The first adults should be seen in our region around May 15, and the last adults around June 15. Then it is over and the last we see of Brood X for another 17 years! 

But already, the nymphs are being reported in Pennsylvania, according to verified observations on iNaturalist.org! The circular burrow openings can be visible now, and nymphs might be visible under protected areas like logs. They are documented to start emerging in mass when the soil temperature reaches 64 degrees F. You can track that yourself as your own science project using a temperature probe or even estimate it by getting the highs and lows for the last few days and averaging them. 

What should people do if they see them? 

Enjoy seeing and hearing them! Take photos and videos to record your observation and their sounds for others to see and hear. If you want to help scientists track where the cicadas are, report your observations to iNaturalist.org and you can provide observations directly to cicada researchers using an app from cicadas.uconn.edu. 

You might have an aversion to insects. In that case if you are in an area where the cicadas are emerging, it will be a difficult time for you for a few weeks. But as I noted, most of us will never see or hear them unless we search them out in other areas. If the flight of the cicadas is disturbing, you might try moving outdoor activities to evenings when the adults aren’t singing and flying around. But remind yourself that in a few weeks they will be gone underground for another 17 years. 

Why are cicadas important for the environment and nature? 

Cicadas provide a good source of food for birds, mammals and insects. For annual cicadas, there are specialized predators such as  the cicada killer wasp. This wasp seeks out the adult cicada, paralyzes it with a sting, buries it in a burrow with a wasp egg laid on it. The cicada will be all the food the wasp larva needs to develop. There are other specialized parasitic flies that track cicadas down by hearing the male cicada singing.

It is thought that these predatory and parasitic pressures on periodical cicadas caused them to have such a long duration between emergences — preventing their predators from being able to build up numbers year to year. These mass emergences every 17 years swamp any impact the available predators can have on the periodical cicadas. 

The cicada nymphs aerate the soil with their burrows and transfer energy from feeding on the tree to them and then to predators that eat the cicadas, an interesting cycle of energy transfer! There is evidence that as the nymphs get large they do drain energy from the tree. But after they emerge and die, their bodies fertilize the trees, and their holes aerate the soil, helping the trees with a growth spurt. 

Are there threats to periodical cicadas? Is climate change affecting cicadas at all? 

Already one brood of 17-year cicadas is no more (Connecticut), and the same goes for one of the 13-year cicada broods. A study done in Indiana tracking cicada emergences over many decades has shown the loss of periodical cicadas from many counties. Periodical cicadas are relying on conditions remaining stable over 17 years, and our rapid pace of development  means they cannot keep up. Once a forest with cicadas is cleared during that 17-year cycle for some development project, that local population is gone. 

It does appear as if cicada emergence is shifting earlier, as our climate warms, and the soil temperature warms earlier in the spring. What impact this emergence shift will have on the cicadas, or other impacts related to this (for example, shifts in tree composition in forests due to climate change) is unclear. Researcher Chris Simon at the University of Connecticut thinks climate warming may increase the number of periodical cicadas emerging one or four years early, and potentially establishing new brood cycles.

Cicada specimens in the Entomology Collection

How many specimens are in the Academy collection?

The Academy of Natural Sciences’ Entomology Collection has cicada specimens from throughout the world and representing at least 150 species. For periodical cicadas, our specimens go back to the late 1800s and include both 13- and 17-year cicada species, identified by the leading researchers on periodical cicadas. One big mystery is the almost complete lack of periodical cicada specimens from Philadelphia, except for one from over 120 years ago. That will be the focus of a separate blog post! 

Text and images by Jon Gelhaus, PhD, Curator of Entomology at the Academy of Natural Sciences of Drexel University and professor, Biodiversity, Earth and Environmental Sciences

P.S. Yes, that first image is a cicada tatoo. No, it is not on the author.


To read more posts in the cicada series, visit

Is Philly Being Snubbed Again?

How to Celebrate 17-year Cicadas — Eat One!


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