Giz Explains: All About Those Noisy Little Cicadas

After a rather lazy 17 years spent relaxing underground, billions of incredibly noisy insects are about to burst out of the earth, noisily swarming over the east coast of North America and wreaking havoc along the way. This is The Great Cicada Invasion of 2013 -- but what the hell is a cicada, anyway, and why have they been hiding for nearly two decades?

So what is a cicada anyway?

Glad you asked! Cicadas are particularly ugly insect: they have prominent eyes and big, well-developed wings. These little fellas are competent flyers. Cicadia are often colloquially referred to as locusts, but that's somewhat of a misnomer. In fact, they're their own peculiar little family of insects, and there are over 2500 species of the critters.

How often do they show up?

So when you hear folks talking about the Great Cicada Invasion, it's worth remembering that they're actually referring to one special type of the insect: the Magicicada, a peculiar little creature that shows up in massive swarms once in a blue moon (or a few blue moons, actually). Swarms of Magicicada -- sometimes referred to as the annual fly or jar fly -- rear up and inflict themselves on the surface of the planet once every 13 or 17 years, depending on their location. The forthcoming invasion is by a group known as Brood 2, that appears every 17 years, and were last seen in 1996. If this all sounds strange, it's because it is: their long period of dormancy still causes scientists to scratch their heads a little.

What the hell have they been doing for 17 years?

Growing! While the 17-year period is a little mysterious, what is known is that Magicicada do take a long time to mature: they spend those 17 long years growing from larvae into their full adult form, feeding on juice from plant roots along the way. Then, the fully grown adults emerge -- literally all at once -- and typically live for just weeks or months, tops.

Scientists have come up with all kinds of theories about how the 17-year lifecycles evolved into being, but it's probably a means of survival: mass-emergence is a survival trait called predator satiation, which sees enough of the bugs survive predation to go on and reproduce, ready to provide the next wave of insects years later. Interestingly, it's been suggested that the fact that the life cycles are both large prime numbers could be another predatory avoidance strategy, which stops those intent on eating them synchronising their own generations to divisors of the cicada emergence period. In other words, prime number life cycles mean that predators can't easily come to rely on their emergence.

When and where will this invasion take place?

Cicadas start appearing, like any sensible creature, when the temperature becomes bearable. Records show that the bugs wriggle out of their shells and take wing when the temperature reaches 18C. The outbreak being branded the Great Cicada Invasion of 2013 is expected to start down in the Carolinas -- furthest South, where it gets warm first -- and then spread north to DC, Philadelphia and New York. The exact timing clearly depends on the weather, but averages suggest that the swarming should start in late April or early May, and finish in the northeast sometime early June. Entomologists expect the cicadas to show up all over the countryside, but also in woodsy suburbs -- and even in urban parks. New York's Central Park is expected to get hit hard, for instance.

Will they cause any trouble?

They're fairly harmless to humans; cicadas don't have a bite or sting, to speak of, but do occasionally mistakes arms for branches. If one lands on your arm and tries to drain you of sap it will hurt a little -- but shouldn't actually do any harm. But they can have a negative impact elsewhere: they can ruin crops and vegetation when females lay their eggs deep in branches, and that's even been known to wipe out local populations of other creatures like squirrels. Oh, and it might pay to have some earplugs handy in May and June: the buzz generated by a swarm can reach 120-decibels, which is about the same noise level as a loud rock show.

And why are they so damn loud?

Sex. No, really: the short adult life of a cicada means that there's a desperate rush for all the creatures to get busy and procreate. To woo their female companions , male cicadas create a loud noise using part of their body called "tymbals" -- complex organs consisting of ribs and membranes, which produce a clicking sound as they buckle back and forth. The resulting, um, song, is loud enough to permanently damage human hearing -- so it pays to keep your distance. Or if you're keen to get rid of the things, consider eating them: in some countries, cicada are considered a delicacy.

Picture: Bruce Marlin