CLEVELAND, Ohio -- The last time Northeast Ohio was overrun by periodical cicadas, Bill Clinton was president, a gallon of gasoline cost about $1.14, and the Cleveland Browns had just returned to the NFL after a four-year absence, selecting quarterback Tim Couch with their first draft pick.

Seventeen years later, beginning next month, multitudes of cicada nymphs that have been growing underground since 1999 are going to crawl out of the earth, returning in astounding numbers of up to 1.5 million per acre, and producing a clamor akin to a chorus of chain saws.

This once-every-17-years phenomenon is cause for excitement among naturalists and in the Metroparks, where cicada walks, talks and a festival are scheduled, and where some of the greatest concentrations of the buzzing bugs are expected to occur.

Visitors will even be able to mark the event with a commemorative cicada T-shirt for sale in the metroparks nature center gift shops.

"It's going to be a wild ride," said Wendy Weirich, director of Outdoor Experiences for the Cleveland Metroparks. "It's like Rip Van Winkle for insects."

For 17 years, the cicada nymphs have been living underground. They began as the size of ants, feeding on sap sucked from tree roots, and have slowly been growing in the deep earth until they reached adulthood.

Somehow - possibly via an internal molecular clock, entomologists aren't sure how - the cicada nymphs determine that 17 years time has elapsed, which causes them to start migrating toward the surface. Once the nighttime soil temperature reaches 64 degrees, eight inches deep for four consecutive days they begin to emerge.

After the nymphs climb into the trees for shelter and shed their exoskeletons, the adult cicadas gradually acquire a shiny black shell with bright orange veins and red eyes.

"There's lots of cool biology elsewhere in the world, but this is something happening here that is really remarkable and unique to this region," said entomologist Gavin Svenson, the curator and head of Invertebrate Zoology at the Cleveland Museum of Natural History.

"These insects are older than 17-year-old kids that have been developing for all of this time underground, and are going to be emerging at the same time."

As this periodical event unfolds, the Metroparks naturalists will rely on public sightings to determine where the largest emergences are happening, which they will use to update their maps and report back to the public, Weirich said.

The so-called Brood V emergence of periodical cicadas actually will consist of three species that look alike, but only can be differentiated by their sounds. All of the emergences will be in the Eastern U.S., beginning in April in the warm southern states and moving gradually northward into June.