While the past year may have made many of us feel cooped up, it’s nothing compared to the Brood X cicadas who spent the past seventeen years underground. When they finally emerge in a few weeks, it will be the brood’s third time above ground since they inspired Bob Dylan’s song “Day Of The Locusts” in 1970.
On June 9th 1970, Bob Dylan visited Princeton University to accept an honorary Doctorate of Music degree. It was a hot day, he didn’t like public events, and didn’t like having to wait for the ceremony to start, but after being prodded by David Crosby he begrudgingly put on the black graduation robe and received his degree.
Even though he didn’t care much about getting a degree, Dylan at least got a song out of the event. It inspired “Day Of The Locusts”, with lines like “There was little to say, there was no conversation, as I stepped to the stage to pick up my degree”. Judging by the song’s lyrics, the main thing that seems to have left a mark on him was the chorus of “locusts” in the distance. What he heard weren’t locusts, though, but the continuous background drone of the Brood X cicadas.
Brood X is one of fifteen still remaining broods of periodical cicadas found in the Eastern United States. Each brood spends the majority of their life underground, but every thirteen or seventeen years (depending on the brood) they emerge all at once, mature into adults, mate, lay eggs, and the cycle starts again a few weeks later when the new generation of cicada nymphs burrow back underground for another thirteen or seventeen years.
Periodical cicadas tend to stay close to home, which makes their emergence highly predictable. Brood X is one of the large broods. It emerges across fifteen states, reaching as far as Michigan, Illinois, and Georgia, but mainly expected to appear in Pennsylvania, New Jersey, Virginia, Ohio, Indiana and Maryland. Any area that had a large emergence of Brood X cicadas in 2004 can expect them again this year.
Some cicadas had an early start. In 2017, Vox reported that a few of the Brood X cicadas had emerged early. But most of the brood remained underground and will come up in late Spring 2021.
Cicada’s emerge all at once as a survival strategy: there is no way predators could get all of them, so that guarantees that at least some of them survive. But how they settled on their schedule is still a bit of mystery. Through simulations and calculations researchers have narrowed down that a prime number period makes it less likely that broods with different periods emerge in the same location. If two broods with different periods produce offspring, the next generation might not all stay underground for the same length of time, and that would put them at risk. Still, it’s not quite clear yet how exactly cicadas emerged to be so synchronized and why they only settled on thirteen and seventeen year periods.
The Brood X cicadas that Bob Dylan heard at Princeton in 1970 died that same year, but their offspring emerged seventeen years later, in 1987. The next generation popped up in 2004, and their offspring – the great-grandchildren of the cicadas that inspired Dylan fifty-one years ago – are currently waiting in the wings.
According to Rolling Stone’s coverage of Dylan’s honorary degree, he was quick to get out of there after the ceremony. “Dylan left the stage, took off his robe and with his party, got into a waiting car and drove on down the road.”
And just like that, Brood X’s cicadas will briefly visit, then disappear again.