Every year, an annual summer symphony emerges. And it comes from the vibrating membranes of cicadas’ abdomens.
The high-pitched buzzing, which often emerges from dawn to dusk, is the males’ mating call, designed to attract the attention of the non-noisy females.
In Pennsylvania, there are 13 species of the insect, most of which appear in the region, and all of whose males sing a different song. (You can hear some of them on songsofinsects.com/cicadas.)
Each species falls into two categories: annual cicadas, which we’re hearing this summer, and periodical cicadas, which swarm by the millions every 13 or 17 years.
Since this year isn’t a brood year — one when periodical cicadas emerge — in the Philadelphia region, you won’t see the density of cicadas that you’d see in a “swarmageddon” year. But what about annual cicadas — are there fewer than usual right now? It was a recent question posed to our Curious Philly platform.
“I have only heard one cicada all summer. What gives?” asked an Inquirer reader.
The answer is unclear. Some experts say there’s no shortage of cicadas, but you could be hearing fewer of them if you live in the city.
“There are a number of species that come out each year, and most likely they wouldn’t all be affected at one time. But cicadas rely on trees, so areas where there aren’t a lot of trees or parks, you’re not going to have many cicadas,” says Jon Gelhaus, curator of entomology at the Academy of Natural Sciences, and professor of biodiversity, earth, and environmental sciences at Drexel University. “The nymphs live underground and feed on tree roots, and many adults stay up in the trees for protection.”
Head outside of the city, and it’s not hard to find a chorus of cicadas humming from the trees. But even so, a decline — whether detectable or not — could be possible. Across the past few years, numerous scientific studies have found decreases in insect health and insect counts worldwide. Cicada numbers aren’t being tracked across the state, however, so it’s not really possible to determine if regional populations are falling.
“It would just be anecdotal stories to say one way or the other,” says Michael Skvarla, assistant research professor of arthropod identification at Pennsylvania State University. “That being said, it might be that cicadas are also experiencing a decline, [and it’s] obvious to people because they’re so loud and easy to notice.”
There isn’t a definitive answer to why insect populations are plummeting globally, but it’s likely due to a combination of factors, “including things like habitat loss and fragmentation, use of pesticides, and climate change”, says Skvarla.
As for cicadas, what’s more conclusive right now: They tend to draw the most attention during brood years — when as many as 1.5 million cicadas synchronously emerge per acre — and that’s not happening in Philadelphia this summer. As for next year? That’s a different story. In spring, “Brood X” is predicted to hit the region.
“They’ll appear in south-central and Southeastern Pennsylvania, including the Philadelphia region, as well as Maryland, eastern West Virginia, and northern Virginia,” says Skvarla. “I’m not sure how abundant they’ll be within city limits, but they should be pretty abundant in more suburban and rural areas.”
No one quite knows why periodical cicadas emerge in mass only every 13 or 17 years, though some experts theorize it may have to do with predator and parasitoid avoidance.
“Regardless, 13- and 17-year life cycles have evolved at least eight different times in the group, so there’s something interesting going on,” says Skvarla.
Annual cicadas, however, emerge every year throughout the summer. Many species are most abundant in July and August, but cicadas will survive through September. Any stragglers will be killed off by the first frost, says Skvarla.
Only about a month of their lives is spent as the adults we hear singing. The first three to five years are spent as nymphs underground.
“When the nymphs come out, they find a place to crawl up, like a tree trunk or a stem of a plant, and hold on to begin the emergence process,” explains Gelhaus. “Its exoskeleton splits along its back, and the adult emerges.”
At this point, cicadas wings are crumply and compacted. They must pump fluid and air into the wings until they expand.
“The whole process usually begins at dusk, and then by early morning, they’re ready to fly off to protect themselves from predators,” says Gelhaus.
Then the mating begins. When ready, female cicadas cut slits into tree twigs and branches to lay their eggs. After hatching, the tiny cicada nymphs drop to the ground and burrow into the soil, where they’ll feed off of roots, grasses, forbs, and eventually trees, until they’re ready to emerge as adults.
As for damage to the trees, annual cicadas cause little harm. Periodical cicadas can cause issues as a result of the mass egg laying, but it’s not nearly as disastrous as tree-feeding insects like spotted lanternflies.
“You get what’s called ‘flagging’ of trees — the point from where the females split the small branches to lay eggs up to the tip of those branches dies,” says Gelhaus. “For the mature trees, it’s not a big deal, but for a newly planted orchard, it could be a problem — a once every 13 or 17 years problem.”
Aside from that, cicadas are harmless. Their symphony may be annoying to some, but the insects don’t bite, and they provide food for an array of other wildlife. They’re also edible to humans.
“I could eat them if I needed to, but it’s not like deveining a shrimp or a lobster,” says Gelhaus. “There’s a lot of exoskeleton, so you’re crunching and crunching on a rather thick exterior.”
But not all find them as unenjoyable.
“I was pleasantly surprised at how much it tasted like a pistachio,” says Gelhaus’ colleague Isabelle Betancourt, an entomology curatorial assistant at the Academy of Natural Sciences.
Also a fan: Gelhaus’ dog George, “the great cicada sniffing dog.”
“My dog loves them. He sniffs them out every year,” says Gelhaus. “As for me, cicadas represent summer. When you hear the first males calling, you know summer is here.”