I have fond memories of the Brood X Cicadas 17 years ago, so I've been excited that my first trip back east since the beginning of the pandemic has coincided with their re-emergence. Brood X is the largest brood of 17-year cicadas and is made up of three distinct species (Magicicada septendecim, M. cassinii, and M. septendecula).
If you think the genus name sounds like magic + cicada,
you're right; and the septendec- part of
septendecim and
septendecula refers to the 17-year cycle. Sadly
cassinii is stuck with the name of a 19th century ornithologist who didn't even discover it;
that honor belongs to Margaretta Morris.
They are about as long as a maple key, although much more substantial (and only marginally better at flying). It's worth noting that although they look and sound a bit like locusts (a type of grasshopper that forms
remarkably large swarms), they are not closely related (grasshoppers, crickets, and katydids are in the order Orthoptera, while cicadas are Hemiptera).
This one seemed to be seeking out the (natural) spotlight.
Periodic cicadas have
awesomely weird—and long—lifecycles. Although they hatch in trees, they immediately burrow underground and spend ~16.5 years developing through five
instar phases (moulting between each one). Periodic cicadas are not the longest-lived insects (
multiple ant and termite species have queens that live 20-30 years), but they do have the longest known juvenile period. They spend most of this time several feet underground feeding on the xylem of plant roots, growing, and developing. Then in April of their brood's emergence year, they make tunnels up to just beneath the surface and wait for temperatures to warm (or at least,
that's the hypothesis, the mechanism is unknown). Then suddenly—all at once over the course of a few weeks—millions of brown nymphs burrow out of the ground, leaving these striking patterns of holes in the ground.
If you walk through the woods (as I've been doing a lot lately, recharging my green-starved soul), you can still see hundreds of tunnels through the compacted soil of the trails.
The fifth-instar nymphs quickly climb nearby trees, shrubs, houses, or other human-made structures. And then just a few hours after emerging from their almost 17 years underground, they shed their exoskeletons one last time, becoming adults. These exoskeletons hang around for weeks stuck to leaves, walls, and more.
I missed the actual emergence, but my mother very kindly shared this photo of a cicada mid-
metamorphosis. Surprisingly, they are mostly white for a brief period of time (minutes or hours?).
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| Photo Credit: Amalia Gnanadesikan |
But over the course of the next few hours and days they develop their adult coloration and their exoskeleton hardens. Ultimately they turn black, with orange legs and veined wings, and (
usually) bright red eyes.
Their wings, especially, take several days to fully harden. They're quite strong for such delicate structures, and they produce lovely shadows.
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| Male septendecim underside and shadow |
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| Female—I think also septendecim? |
And then finally the adult cicadas climb up into the trees and fly about looking for mates.
The cicadas have been out in force this past month in both Maryland and New Jersey. You can see them everywhere—both alive and dead—although, their density is highly variable. Some streets and trees seem full of them (and their impressively loud screams), while others seem comparatively empty. For a while, if I saw movement out the window, it was more likely to be a cicada than a bird! This individual in Princeton's Prospect Garden was particularly cooperative in posing on this lovely color-coordinated day lily (something else I've missed, living in Arizona).
In person, I didn't see the details of the legs, but sorting through my photos later, I was intrigued to see the texture of the legs, particularly the v-shaped hooks on the tips.
Only the males "sing" (they have dedicated organs, called tymbals, on their abdomens that produce sound), and the different species each have their own song. Septendecim has the most iconic call, starting on a higher pitch and then falling off; it really sounds like they are screaming. When enough of them are chorusing together, however, it sounds like a loud whirring or electronic hum (maybe as if you were onboard the Enterprise). When they join together to form a chorus, they can reach 80-90 dB (about as loud as a passing truck or a hairdryer). Apparently the loudest trees are often full of M. cassinii, which are particularly synchronized. However, like other cicada species, all Magicicada species sing only in the daytime and when it's relatively warm. They take a respite in cold and wet weather.
Theses species-specific calls help cicadas find their mates, after which the females lay their eggs in trees. This often kills a small part of the branch—a process referred to as flagging—which you can see in many trees of various species wherever the cicadas are abundant, but this does not harm the rest of the tree.
And then—having lived for all of a few weeks—the cicadas die, littering the ground, sidewalks, roads, and more. It's difficult around here not to find them if you look hard enough. And sometimes you really don't even have to try.
You'll even encounter stray wings decorating the ground.
I thought this one looked a bit like it was riding a broomstick—magic indeed!
Our cats have been rather intrigued by the cicadas (mostly when we let them out on the deck), although maybe not quite as intrigued as I've been myself.
In a few more weeks, the eggs will hatch, born as ant-like nymphs that will tunnel underground and start the cycle over again, to be seen in another 17 years. I, for one, look forward to it!
