The Northern Illinois brood, called XIII and coming out every 17 years, is extra dense, with as much as 1.5 million bugs per tree-covered acre - which is nearly a billion per square mile - in some places like Ryerson, Kritsky said.
Illinois hit with cicada chaos. This is what it is like to see, hear and feel billions of bugs
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Brood X got so loud that in 1902 at Arlington National Cemetery that they almost drowned out President Theodore Roosevelt, who was known for his booming speaking voice, Kritsky says.
EXPLAINER: What are cicadas and why do they bug some people?
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