Soon this spring - no one knows when - one of nature's oddest, and noisiest, spectacles is set to unfold.

Billions of cicada nymphs, lurking underground for 17 years, are set to emerge as if on cue and begin climbing any upright object they can find.

But precisely where exactly they'll show, no one is certain.

Call it Swarmageddon: Rise of Brood II.

The 'Brood II' cicadas (genus: Magicicada) are different from the annual cicadas you might hear on summer nights. Not only do they look different, but their numbers dwarf the annual insects.

"This is one of two big broods we have," said George Hamilton, a Rutgers University professor, and chairman of the Department of Etomology.

He said Brood II, when it last emerged in 1996, saw its highest densities in northern New Jersey. So, it's unlikely the immediate Philadelphia area would experience a large population, but no one is sure.

"It's kind of hard to pinpoint exactly where they're going to come out," Hamilton said, explaining that much of it has to do with where humans have since developed. Cicadas disappear as development encroaches.

Fortunately, the cicadas themselves are not particularly destructive. Although they insert their eggs in new tree branches, they do not strip foliage as do gypsy moth caterpillars. They are often confused with locusts, which are really grasshoppers.

The 17-year, Brood II cicadas, traced to their first observed local emergence in 1894, are a little less than two-inches long. They have bluish-black bodies, reddish eyes, and some of the wing veins are orange.

And, they make noise.  Lots of noise - a whirring, raucous sound produced by males through tymbals - organs on their abdomens.

They lay their eggs in trees. The eggs drop to the ground, yielding nymphs that burrow as much as two-feet deep and grow underground for another seven or eight years. They continue to feed and develop until the spring of their 17th year.

Several weeks before emerging, they build small cones that stick above the soil. The nymphs emerge together one night in vast numbers, walking towards trees and standing objects. Once they climb, they split their nymphal skin and emerge as adults.

The last 17-year brood to emerge was most noticeable locally in Gloucester County, according to a database kept by magicicada.org, a website dedicated to tracking cicadas.

Incidentally, the last 17-year brood to hit the area was known as Brood X in 2004. Princeton was so flooded with cicadas that they covered trees, bikes and just about any stationary, upright item on campus.