Entomologists say they want endangered species protection for a recently rediscovered butterfly that experts believed had been extinct for more than 50 years. Paul Hammond, an Oregon State University entomologist and butterfly expert, said he rediscovered the butterflies by accident. ``In the spring of 1989 I hiked out onto a south-facing slope of a hill that had native prairie on it, and here was this very unusual kind of lupine plant with all these little blue butterflies swimming around on it. ``I knew immediately what it was,'' he said. It was Fender's blue butterfly, a relic of the ice ages found only in Oregon's Willamette Valley. The butterfly was last seen near the small town of Wren, west of Corvallis, in 1937. Since that find last year, several pockets of the species have been found in western Oregon. A petition is being prepared to ask the U.S. Fish and Wildlife to declare the butterfly a threatened species under the federal Endangered Species Act. Hammond said the butterfly has a wingspan of only about 1 inch. The male is a ``brilliant, iridescent blue,'' he said. ``They really stand out. The female is a drab brown.'' The butterfly dates back more than 10,000 years, Hammond said. Surrounded by glaciers to the north and mountains to the south, east and west, the butterfly's habitat was limited to a small area of the Willamette Valley.