Trillions of Brood X cicadas emerge from the ground for first time in 17 years

ITV News Correspondent Robert Moore reports on the phenomenon that sees trillions of insects emerge from the ground every 17 years in parts of the United States

Words by Washington DC Producer Natasha Tierney

Trillions of red-eyed insects emerging from underground after being buried for 17 years might sound like something from a sci-fi film, but that's exactly what's happening on the east coast of the US right now.Residents there have been eagerly anticipating the mass emergence of the brood-x cicadas, a natural phenomenon last seen in 2004, for several weeks now.

"You're literally seeing tens of thousands of periodical cicadas ' - Prof. Michael J. Raupp, Entomologist at the University of Maryland watches as the insects emerge from the ground

So what exactly are these unusual creatures?Brood X is the name of one the largest groups of cicadas in North America, which come out in the eastern United States for a few weeks every 17 years. Unlike most cicada species, which come out annually, the US is home to several 'periodical broods', groups of cicadas which stay underground for 13 or 17 years. These rare insects are found in just three countries - India, Fiji as well as the United States, which is home to seven of the nine known species.

"From here they fly to the treetops before making a loud chorus" - Prof. Raupp on the male's distinctive mating call

"Brood X is one of the most amazing phenomena on planet earth," says Professor Michael J. Raupp, an entomologist at the University of Maryland."For millions of Americans, you don't have to go to Tanzania, you don't have to go to Botswana - you can go right in your own backyard and have a cicada safari."

Where are they being found?Brood X cicadas are emerging in 15 US states and Washington DC between mid-May and the end of June. There are thought to be as many as 1.3 million cicadas per acre in the main hotspots.Typically they start to crawl out from their underground tunnels only when soil temperatures beneath the surface reach 18C, and this year's cooler weather is thought to have slowed things down.

Nonetheless, large groups of adult cicadas are already being seen in Georgia, Kentucky, Maryland, North Carolina, Pennsylvania, Tennessee, Ohio, Virginia and Washington DC. How long do they stay above ground for?When they finally make their way out after 17 years below the surface, the nymph cicadas climb onto plants and other vertical structures, before shedding their exoskeletons and inflating their wings. After a few days, their shells harden and mating can begin. The males fly up to the tree tops to call the females with their signature chorus. Once they've found their match, the female cicadas signal their interest by clicking their wings.

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They mate in the treetops before the female flies off to lay her eggs in small nests that she cuts into branches and stems."Each female will lay between 400 and 600 eggs, so you can see the potential for population growth", says Professor Raupp. The adult males die shortly after mating; the females once they've laid their eggs. But once the eggs start to hatch, a new generation of nymphs will crawl down underground and settle in for the next 17 years. The whole process takes around four to six weeks. 

What do they sound like?Periodical cicadas are famously loud. The calls of just one group of males can reach 90 decibels - about the same noise level as a motorcycle, or aeroplane approaching for landing. Their loud choruses have even been known to disrupt weddings and other outdoor events. In 1970, Bob Dylan supposedly wrote the song Day of the Locusts after brood X interrupted him being awarded an honorary degree at Princeton University.

"From here they will fly up into the trees and bigger to make a loud chorus - Prof. Raupp on the cicadas very distinct mating call

Why do they only come out every 17 years?

The cicadas know when to emerge through their internal body clock and environmental cues, such as the flow of sap through the tree roots. How they determine exactly what year it is, however, remains a mystery to scientists."Why every 17 years is the million dollar question," says Professor Raupp.

"By having a very long life cycle they can evade their predators. No bird or small predator lives for 17 years.  "For their strange strategy of survival which we call 'predator satiation', they must emerge simultaneously in such vast numbers that they fill the belly of every predator that wants to eat them, and there's still enough left over to perpetuate their species."

Are they dangerous?Cicadas are harmless to humans and animals, and don't bite or sting. They provide vital nutrients for plants and soil when they die, and are a rich protein source for birds and other predators during their brief spell above ground.Many scientists and nutritionists believe insects like cicadas could be the sustainable protein of the future for humans as well.Several restaurants and chefs are already making the most of the rare brood X emergence by serving up cicada dishes, and posting recipe ideas on social media.