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People often fondly recall the hypnotic buzz of locusts on the soundtrack of their youthful summers. But it is cicadas, not locusts (a type of grasshopper), whose buzzing we hear during the dog days of summer. The annual “dog-day cicada” (Neotibicen canicularis) will emerge once again in mid-July to buzz, mate, lay eggs and die within a few short and noisy weeks.
Summer trivia: “Dog days” refers to a period of warm weather coinciding with the appearance of Sirius, the dog star, in the constellation Canis Major (“Greater Dog”). In our northern hemisphere, dog days occur between about July 3 and Aug. 11.
Mysterious Biological Clock After spending three to seven years underground as nymphs, sucking a substance called “xylem” from tree roots, dog-day cicadas feel the urge to emerge. Some believe soil temperature alerts them when it is time, but the trigger for their emergence is still a scientific mystery.
Nymphs burrow out of the soil at night, climb up their host tree (or a fence or nearby building), and start shedding their protective exoskeleton. As the nymph swells with life-giving fluids, its exoskeleton splits and a ghostly green “teneral” (not quite mature) adult gradually wriggles out. Fluid pumps into its wings, which unfurl and must dry out completely before the mature cicada (now called an “imago”) – with its big black eyes and green/brown body – can fly off to find a mate, leaving behind the familiar empty brown shell.
Cautious Crooning and a Wicked Wasp
After settling on a high tree branch, never more than half a mile from where they emerged, males sing their love songs and wait for females to accept their bug-eyed suitors with an audible wing flick. The sonorous mating call – created by vibrating abdominal membranes called “tymbals” – has been likened to “a circular saw buzzing through a plank of wood in a neighbor’s garage” by Dan Mozgai, creator of the website Cicadamania.com. Dog-day cicadas start their shrill crooning late in the afternoon and into dusk, when predators such
as birds are less likely to be on the hunt.
One of the annual cicada’s grisliest predators is the cicada killer, a formidable ground-dwelling wasp that is more interested in finding cicadas than stinging humans. The female cicada killer paralyzes its victim, then lays eggs within its body. When the eggs hatch, the grubs feed on the still living cicada.
The Beat Goes On
Not long after a cicada pair mates, the male dies and the female sets about laying up to 600 eggs in numerous slits she makes in twigs and branches before she also dies. In a few weeks, the eggs hatch into rice-sized nymphs which drop to the ground, burrow into the soil, and patiently await their own emergence in several years. And so it goes summer after buzzy summer.
Bashful vs. Bold: A Tale of Two Cicadas
Despite their noisy attempts to attract a sweetheart, harmless dog-day cicadas are rather shy, says Philip Nixon, Ph.D., an entomologist with the University of Illinois Extension, which offers educational programs to Illinois residents. We are more likely to hear than see these well-camouflaged insects, he says, which may move sideways around a tree trunk if they become aware that someone is paying attention them.
“It’s an avoidance maneuver,” explains Dr. Nixon. “The annual cicada is very secretive, and they are cagier about being seen than periodical cicadas.”
Indeed, periodical magicicadas – the ones that appear in 13- and 17-year cycles – are more assertive and flamboyant, singing boldly during the day and sporting bright red-orange eyes and shimmering golden wings that stand out against their black bodies. Though an easy target for predators such as birds, rodents, snakes and bats, their huge numbers guarantee abundant mating opportunities to ensure millions of future offspring.
“They seem to have this crowd mentality – they don’t worry about avoiding capture or being eaten,” says Dr. Nixon, “like they’re saying ‘we’re still going to reproduce like it’s going out of style.’ Numbers work in their favor.”
In four years, millions of periodical cicadas will surge out of the ground, shattering sound barriers – or at least rattling our eardrums – with their strident love songs. According to Dr. Nixon, a doughnut-shaped area surrounding Chicago that includes Cook and the collar counties will be mobbed by 13-year cicadas in 2020, followed by an even larger appearance of 17-year cicadas across all northern Illinois in 2024. Each cacophonous emergence will begin around Memorial Day, with the last females dying off in mid-July.
Longing for the Buzz?
People who miss the buzzing because they have no cicadas often ask Dr. Nixon if they can collect some of the insects for their own yards, hoping their kids can experience the unique sound of summer, too.
“Attempts at transplanting cicadas are very unlikely to result in established populations,” says Dr. Nixon. “The transplanted cicadas would be few enough to probably be eaten by birds before they laid eggs. If they were successful in laying eggs, the numbers emerging 13 or 17 years later would be too few to avoid essentially total loss through predation.”
Those folks could certainly visit Evanston in July, for an earful of dog-day cicada serenades. And if that’s not enough for them, they’re in for a riotous treat in 2020.