People left horrified as trillions of cicadas swarm towns in ‘biggest invasion in centuries'

People across the US have been left horrified as trillions of cicadas swarm towns in what's being dubbed the ‘biggest invasion in centuries'.

Those in the southwest of the country were told to expect a 'sight to behold' as experts predicted something pretty big on its way back in April.

Periodical cicadas - which usually surface every 13 years - are emerging with another brood which appears in a 17-year cycle.

Annual cicadas, typically bigger and greener, can be found anywhere in the world.

But the more interesting periodical bugs, which are black in colour and have very distinctive red, bulging eyes, can only be found in North America.

The dual emergence of the periodical cicadas makes for a rarer occasion. In fact, such an event is estimated to have happened last some 221 years ago in 1803.

So, how can you spot these periodical cicadas?

Well, aside from a distinctive look, they are extremely loud so can be heard from a mile away, literally.

University of Connecticut cicada expert John Cooley dubbed the invasion currently taking American by storm as 'cicada-geddon'.

Brood XIXs first began the storm as they spread through the Midwest, including Iowa, Illinois and Indiana.

On top of that, they've also spread in the southeast, in smaller sections of the likes of Alabama, Arkansas, Georgia, Kentucky, Louisiana, Missouri and Mississippi, according to National Geographic.

Following that is Brood XIII, first surfacing in Illinois, with these species appearing every 17 years.

Speaking of the phenomenon, Georgia Tech biophysicist Saad Bhamla said: "We've got trillions of these amazing living organisms come out of the earth, climb up on trees and it's just a unique experience, a sight to behold.

"It's like an entire alien species living underneath our feet and then some prime number years they come out to say hello."

Well, the invasion has a lot of Americans freaking out, with many people's experiences of the swarm going viral on social media.

One particular TikTok video documented a worker operating a power saw while covered with well over a dozen of the large bugs.

“We [are] out here fighting for our lives!” the natter terrifyingly says. "These cicadas have taken over."

Researchers at the University of Connecticut have predicted the cicadas will cover as much territory as the size of the US state of Delaware.

"If we accept an estimate of a million cicadas per acre and if the total combined area of a periodical cicada emergence is roughly the size of Delaware, then more than a trillion cicadas will be involved," the research states.