Natures wonders: 17-year Cicada lifecycle (Introduction)

by David Turell @, Monday, May 09, 2016, 02:52 (1516 days ago) @ David Turell

An amazing series of metamorphoses over 17 years:

"Like the biblical pests, cicadas do occur in scary numbers.

This month, millions—or maybe billions; they're hard to count—will surface primarily in Ohio and West Virginia when one of North America's 15 broods tunnels out of the ground for the first time in 17 years.

“'The most dense I've ever measured is 356 per square meter,” said Gene Kritsky, chair of biology at Mount St. Joseph University in Ohio who counts cicadas in sample areas by inserting the handles of spoons into the finger-size holes left by the emerging insects and then tallies the spoons as he removes them. “It's not inconceivable we could have 6 billion cicadas.”

"Cicadas live most of their lives underground in deciduous forests in the eastern half of the U.S. Twelve of the 15 known broods emerge from the ground after 17 years. The other three emerge after 13 years. There is some overlap, but the broods that take longer to mature tend to be located farther north.


"After surfacing, the insects spend several weeks in a buggy bacchanal of singing, mating and laying eggs before they are eaten by predators or simply drop dead. The entire event lasts six weeks or so.


"The life cycle begins anew when the eggs hatch about six to eight weeks later, and the tiny nymphs, measuring just 2 millimeters, drop to the ground. Many will be consumed by spiders, ants and beetles, but those that manage to burrow into the earth will live safely below the frost line, where the temperature hovers around 50 degrees Fahrenheit, for the next 13 or 17 years, until they emerge for their own coming-out party.


"Underground, the nymphs will molt four times. When they emerge, they molt a fifth and final time, leaving behind browns husks of exoskeletons clinging to trees and other surfaces before spreading their adult wings. The complete transformation takes about three hours.


"No one knows exactly how the nymphs keep track of the years while underground, and occasionally, some do appear to get confused, emerging either four years earlier or four years later than expected. But for the most part, they are remarkably accurate, heading for the surface with their brood in the appropriate year when the soil temperature consistently registers 64 degrees Fahrenheit, signaling the arrival of spring.

"And unlike locusts, cicadas, overall, are beneficial to plants.

“'By coming out of the ground, they open up a lot of holes the size of an ordinary person's first finger that allow air and water and nutrients to suddenly go deeper and quicker in the soil than before,” said Thomas E. Moore, curator emeritus of the Museum of Zoology at the University of Michigan. “We wouldn't have the same kind of forests if we didn't have them.'”

Comment: How did Darwin-style evolution arrange the development of this strange complex lifecycle? I doubt it did.

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