Riverbanks Zoo and Garden is like a slice of rain forest tucked among the downtown skyline of South Carolina's capital city, the Saluda River and a busy freeway to the suburbs.

With more than 15 million visitors since opening in 1974, the zoo is the largest public attraction in South Carolina and has been ranked among the top five North American zoos for its support of programs of the American Zoo and Aquarium Association.This summer, for the second year, the theme of this 170-acre zoo is butterflies.

"Jewels of the Sky," a 3,200-square-foot butterfly garden, features swallowtails, monarchs, painted ladies, zebra longwings and other varieties. They fly freely through the screen-encased exhibit and sometimes even land on visitors.

The winding swath of trees and flowers is made up of butterfly-attracting varieties such as lantana, bottlebrush and milkweed.

"We've come to realize, just as amusement parks that add a new roller coaster or exciting exhibit every year, the public expects it," said zoo spokeswoman Mary Leverette. "This gives us an `oomph' for the season."

The butterflies at Riverbanks arrive from The Butterfly Farm in Florida as chrysalises, the cocooned stage between the larva and adult, and are put in a display box for visitors to observe.

The butterfly garden idea evolved from a trip to the Vancouver Aquarium.

"A few butterflies flew through the reptile exhibit and people were more interested in the butterflies than the crocodiles and snakes," Leverette said.

The butterflies here live only about a week, but a steady supply of new ones means there are always 300 flying in the exhibit.

Riverbanks' permanent collections include an aquarium and reptile complex, an African plains exhibit and mammal complexes. About 200 mammals, 300 birds, 300 reptiles and amphibians and 1,300 fish live at Riverbanks.

A 55,000-gallon aquarium filled with sharks, moray eels and other Pacific species is a highlight of the tropics and ocean gallery. Feeding time at the sea lion and penguin exhibits is another crowd pleaser.

Five years ago, Riverbanks was named the 1993 Travel Attraction of the Year by the Southeast Tourism Association and three years ago it added the $7.2 million, 70-acre botanical garden across the river with walking trails, a rose garden and a walled garden reminiscent of a Spanish hacienda.

"All rolled into one, we're not the biggest, not the most expensive, but what we have is top-notch," Leverette said.