by Janet A. Ginsburg

I am being serenaded by cicadas and it is glorious. They are the sound of summer,

the neon hum to the flicker dance of lightning bugs on warm humid nights. Cicadas are everywhere and nowhere. How can something that loud and large be so hard to spot?

Cicadas are my favorite. Dinosaurs listened to cicadas. And before them, lizards, amphibians and other insects of the Permian, more than 250 million years ago, back when Pangea wasn’t even quite Pangea yet. Cicadas have survived global extinctions, ice ages and the asphalt spread of urban sprawl. Summer after summer they survive hordes of hungry predators in a desperate and daring dash to the treetops for a few brief weeks of uncorked noisy revelry, a blow-out party after years of silent preparation.

Scientists know quite a lot about cicadas: The meanings of their songs. Their diva-worthy requirements that soil temperature be at least 64 degrees Farenheit to emerge and the air temperature be at least 70 to sing. Their romantic ardor for lawn mowers and leaf blowers. The male’s use a pair of abdominal ridges called tymbals to make noise (wings are for flying, don’t you know… although females will use them occasionally for a little “Over here, honey!” signaling).

Still, cicadas have managed to hold a few secrets close.

Each fertilized female can lay hundreds of eggs in tree branches, which means the first order of business for the tiny newly hatched larvae is to literally take a flying leap into the unknown. It’s the fastest way down and they have no time to lose. They have to dig into the ground and start feeding on tree roots before the weather above turns frosty. And yet, though there must be millions of larvae, I can’t recall seeing a single one in mid-leap. Or even splat on the pavement, blown by the winds to an unfortunate end. Maybe they do it at night. Maybe they hide in the glint of the sun. Or maybe these nymphs really do have magical powers and simply turn themselves invisible.

The most enduring mystery, of course, is why a few species in the fabulously named genus Cicada Magicada, all of which live east of the Great Plains in North America, emerge only once every 13 or 17 years. No one really knows how this buggy homage to prime numbers got going, but theories abound -- the most popular being that it's a predator defense. A cicada emergence on this scale is a once on a lifetime feast for predators whose own life cycles are annual, or peak at two, three or even four years. The glory of an odd prime number is the guarantee that emergence will rarely coincide with more two of these predator cycles. And predator populations bulked up on easy cicada dining are bound the crash back to more manageable levels in the interim.

Alright, all relatively recent glitches for which our heroes have had little time to adapt... But what was a 13 or 17-year cycle adapted to in the first place? Some speculate it could be a vestige of climate change at the end of the Pleistocene. As North America warmed up and glaciers melted, cicada populations that had expanded into new areas may have found themselves stuck underground for years longer than usual, waiting for the soil to warm up to that magic 64 degrees. Perhaps as long as 17 years. And the ones that survived could have had their internal clocks forever reset.

As for predators, is there anything that doesn’t find cicadas tasty? They’re like the chocolate of insect treats. Everything from squirrels, skunks and raccoons, to possums, birds and coyotes – all of which are thriving in cities and suburbs – adore these grubby little delicacies, methodically patrolling lawns and gardens with the earnestness and greedy expectation of kids on an Easter egg hunt. It is hard to believe overall predator numbers shift that much from year to year, even if some predator populations get a cyclical boost every few years. There are just so very many hungry mouths.

There is also a predator from which no amount of clever maneuvering can escape: a fungal parasite that has built its whole life around Magicada: Massospora cicadina, the 13 (or 17) -year fungus… The first cicadas of the season to be infected develop asexual spores, which eventually explode through the insects’ abdomens to infect other cicadas. This second group develop sexual spores, and round and round it goes.

Yet the vast numbers of cicadas in these periodic synchronous “broods” are so overwhelming that more than enough survive to ensure the future of the next 13 or 17-year generation. The pattern, however it may have started, continues because there is not enough pressure for it to stop.

Beyond the why, there’s a question of how. How does an insect with a brain the size of a speck count, much less count to 13 or 17? That’s more than we require of kindergarteners.

The short answer? They take a cue from trees. A particularly clever team of researchers at the UC-Davis discovered that 17-year nymphs sucking on roots of orchard trees that had been artificially forced into two foliage cycles per year emerged at the 17th cycle, even though technically only 8 ½ years had passed (abstract).

That still doesn’t explain exactly how cicadas count to 17 (or 13), although the suspicion is it's somehow hard-wired into their biology. Cicadas may not even count strictly by ones. Some think they could be counting by fours, with a one year add-on:

(3 x 4 ) + 1 = 13 and (4 x 4) + 1 = 17.

On a molecular level, there’s not much difference between 13 and 17-year species. And suspiciously, if a 17-year cicada emerges early, it is almost always by either four years or one year. It is possible, then, that 13-year cicadas could have developed from some early-emerging would-be 17-year bugs.

Next year, Brood XIII (ironically, a 17-year brood) will emerge in Chicago – my neighborhood – as well as parts of Michigan, Wisconsin and Iowa. A few must have popped out early because it’s been a pretty thunderous season. The motors of August cicadas -- so loud, so summer, so right now. But also a sound of the deep past, of patience and of time itself. This is just a warm up band for the chorus to come.

I can’t wait.