The last time the US saw the two broods of periodical cicadas emerging at once is thought to have been back in 1803, when Thomas Jefferson was president.



Trillions of cicadas are about to emerge in parts of the US in numbers not seen in decades and possibly centuries.



People in the southeast of the US are set for a "sight to behold¹", experts say, as periodical cicadas - which usually surface every 13 years - will emerge coinciding with another brood which come out in a 17-year cycle this spring.



While annual cicadas, which are bigger and greener than their black-bodied cousins, can be found anywhere in the world, periodical bugs², which are black in colour and have red, bulging³ eyes, can only be found in North America.