- April 16, 2024
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This summer, the United States will host one of nature’s wildest concerts filled with sex, drugs, and rock’n roll. The stars of the show? Billions of cicadas that have been hiding underground for up to 17 years.
The life cycle of cicadas is one of the most intriguing sagas in the animal kingdom, filled with mysteries that perplex evolutionary biologists.
Perhaps the most dramatic example is the group of species known as “periodical” cicadas—these insects spend 13 to 17 years of their life in solitary confinement underground to emerge in the billions for one month of summer.
We won’t see periodical cicadas in north-central Florida, but most Palm Coast residents are probably familiar with the competing bands of our local cicadas, from the zit-zit-zit-zit of the seaside cicada to the soft buzz of the swamp cicada that crescendos and pulsates and then finally tapers off in a diminuendo in the early mornings.
Chances are you haven’t seen these cicadas.
Even if you have, you may not be able to tell one species apart from another, many look so alike. And yet each species has its own distinct song.
“Of the nearly 200 species of cicadas found in the United States, you can count on one hand the lifecycles we know about in any appreciable detail,” said Brian Stucky, a scientist at the University of Florida who earned his PhD studying the relationship between cicadas and parasitic flies. “There’s still so much to uncover.”
Most cicadas hatch from trees and fall to the ground, where they burrow in and spend up to 99.7% of their lives as nymphs, initially about the size of ants. Underground, they seem to lead a pretty dull life, sucking up sap from the xylem of tree roots.
If you lived the cicada lifecycle, you would spend about 78 years and 10 months in your eccentric uncle’s underground bunker, then emerge for two months to search for and hopefully find your soul mate before you die.
For some context, the average human lifespan is approximately 79 years. If you lived the cicada lifecycle, you would spend about 78 years and 10 months in your eccentric uncle’s underground bunker, then emerge for two months to search for and hopefully find your soul mate before you die.
“The question is how and why do periodical cicadas have such a unique lifecycle with such a tight synchrony?” Stucky said. The current hypothesis supposes that periodical cicadas evolved this lifecycle as a means to avoid predation. Basically, most predators would die off quickly if they waited for cicada broods to emerge. You would starve, too, if you had to wait 13 to 17 years between meals.
No one knows exactly how cicadas can tell when it’s time to emerge. One key factor is soil temperature, but this doesn’t account for the years-long timer.
There is some evidence that changes due to global warming and human development may disrupt soil temperature, thereby affecting the timeline for when cicadas emerge.
Whatever the main switch, the emergence of cicada broods can be dramatic.
Young nymphs claw their way to the surface, hook themselves at the base of a tree, and molt one last time, leaving an empty husk of their old selves as they emerge into adulthood and fly off. You may see these husks clinging to the bark of trees and mistake them for the insects themselves.
The next 4 to 6 weeks of a cicada’s life is spent in a frenzied orgy as they search for mates to begin the cycle all over again.
The method of attracting potential mates? Making lots of noise.
Construction workers sometimes say that cicadas are drawn to the noise of their equipment. One report says that some species of cicadas can produce a sound in the 100-decibel range, the same sound intensity as a jackhammer.
“Cicadas make sounds for two main reasons: to attract a mate and to startle predators,” said Stucky.
Males will congregate into choral groups, maneuvering special organs on their abdomens that have evolved specifically for making sound. These organs, called tymbals, consist of a ribbed membrane that is stretched taught like a drum.
Specialized muscles attached on the inside of the membrane will contract, collapsing the ribs. When the muscles relax, the ribs snap back into place, producing a clicking sound.
“It’s like if you squeezed an empty soda can in your hand and then let go,” explained Stucky. “Then when the can snaps back into place, it makes a crinkling sound. That’s essentially how cicadas make their songs, only it’s happening dozens of times per second. To our human ears, this sounds like a continuous buzzing.” In general, only the male cicadas sing.
One report says that some species of cicadas can produce a sound in the 100-decibel range, the same sound intensity as a jackhammer.
Females may be mute, but they are acute listeners. They’ll listen to the different musical arrangements—a cacophony of discordant sounds, like trying to pick out the voice of Ed Sheeran while Josh Groban and Louis Armstrong and Billy Joel imitators are all singing different songs.
No one really knows what makes one cicada’s song stand out from the rest, whether females prefer volume or intensity, pitch or timbre.
When a female hears something she likes, she’ll find the crooning male herself. In some species, females will flick their wings at the males to catch the attention of their future lovers.
As you might imagine, all that ruckus also attracts unwanted attention.
Parasitic flies such as Emblemasoma erro listen for the male cicada’s song. A pregnant female fly will then stalk the cicada, waiting, biding its time.
When the cicada takes flight, the fly will zip out—“Faster than you’re able to see,” Stucky explained—and in mid-flight the fly will dip down its abdomen, depositing its living larvae to burrow into the cicada’s body. The larvae will eventually eat the cicada from the inside out.
“For the most part these flies parasitize male cicadas,” Stucky explained, “but there are a few cases where female cicadas were also parasitized, quite possibly because both the female cicada and the female fly were attracted to the same male cicada.”
These parasitic flies have been documented to infest swamp cicadas right here central Florida. It’s unclear whether these flies attack periodical cicadas.
Periodical cicadas have an even more specialized parasite, one that has actually managed to synchronize itself to their 13-to-17-year lifecycle, rendering their primary defense useless. This predator is a fungus, Massospora cicadina.
This fungus also prefers male cicadas, creating a yellow plug of fungal spores that replaces the cicadas’ abdomens. The spores hijack the male cicada’s nervous system and causes him to flick his wings.
This behavior is often used by female cicadas to attract a male during mating, meaning that the Massospora fungus manipulates its dying victims to lure other males close enough for the spores to spread.
While the effects of Massospora are devastating to periodical cicadas, the fungal spores are harmless to humans and their pets.
Cicadas themselves are harmless — they don’t bite or sting, nor do they damage property or eat our crops.
Early settlers of North America thought of cicadas like plagues of locusts described in the Bible.
While their sheer numbers may seem biblical and their sounds may be a persistent reminder of an unseen presence, these insects keep to themselves.
They don’t have time for anything else. For insects that only spend a fraction of their lives above ground, they’re focused on one thing only: find their soulmate and make babies.
“The lifecycle of these insects is really amazing,” Stucky said. “They live quite a long time, but so little of their life is actually known by humans.”
So when you walk outside and hear that constant, rattling trill of the lyric cicada in your backyard, think of the short flings happening across the stage of the whole United States. Maybe take a break from thinking about the buzz of your own short life and take a moment to enjoy nature’s summer symphony.
