Cicadas show up four years early in the U.S. Here's why
Thursday, May 25, 2017, 2:29 - Some 17-year cicadas have emerged four years earlier than their scheduled return in 2021 after reports of sightings filed in several states in the U.S. over the last few days.
Researchers divide the populations of cicadas into broods. The sightings reported in Tennessee, Washington D.C., Ohio, Delaware, Indiana, Kentucky, Pennsylvania and New Jersey are believed to belong to Brood X, a 17-year species. Those from Brood X should emerge in 2021.
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Experts conclude that cicadas must have an inborn molecular clock, and they might be able to tell the time based on the changes in tree biology as they feed on tree roots. Cicadas are also only known to emerge after soil temperatures reach above 64 degrees Fahrenheit.
However, it is estimated about up to 10 percent of the total Brood X cicada nymphs will come out earlier than the rest. These are known as stragglers.
If a large number of cicadas do emerge over the next few weeks and successfully mate, a new brood of cicadas may be established and are expected to emerge in 2034.