A double cicada invasion is set to "utterly cover" parts of the United States, an ecologist has told Newsweek.
The long-anticipated swarm of cicadas has already begun, with the insects emerging from their broods in the southeast. Cicadas have been spotted surrounding trees in Charlotte, North Carolina, local news outlet KKTV reported, and the sight is set to become more common in the coming days.
The so-called invasion is to being caused by two broods that usually live underground, emerging at once.
James Loving Lichtenstein, an assistant professor in biology and evolutionary ecologist at Sacred Heart University, told Newsweek that "they will utterly cover Illinois and much of Missouri and Arkansas."
"They'll also show up in eastern Iowa, southwest Michigan, northern Alabama and Georgia, and the western end of the Carolinas," he said.
However, although many of the insects are emerging, Lichtenstein said the insects have always been around.
"The cicadas have always been here, living underground, drinking sap from tree roots," he said. "All cicadas living underground feeding on roots for some years then emerge in the summer to find mates and continue the cycle. What makes periodical cicadas special is that they all emerge at the same time every 13 or 17 years depending on the species. Because they all emerge together, they emerge in huge numbers.
"This is thought to overwhelm predators (they can't possibly eat everybody). You could say that the need to avoid predation is what causes them to show up in swarms. They have been doing this for millions of years. Large groups of them emerge together over these large geographic areas at the same time. These are called broods."
In fact, this particular phenomenon, where two broods emerge at the same time, has not been seen in around 200 years.
Cicada broods develop underground over several years before emerging. When they make their way above ground, they usually stay there for around a month and reproduce.
These periodical cicadas are native to North America, and come up around every 13 to 17 years.
Although seeing so many of the insects emerging at once may be unsettling, Lichtenstein said that they "pose no danger to human beings."
The so-called invasion will cause some damage, however, mainly to trees.
"They make small cuts to living twigs to lay their eggs. To mature trees this is a nuisance. To small trees this can be a real threat," Lichtenstein said. "People living in the brood areas might want to cover their newly planted trees with some sort of insect netting. There is no point trying to poison them because survivors will just show up in their place."
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