Sanchez-de Leon thinks the 6-inch-long version she found - a little longer and fatter than a common nightcrawler earthworm - might be a young adult.

One reason so little is known about the giant earthworms is, well, they're worms.

Unlike the celebration touched off by last year's sighting in Arkansas of the ivory-billed woodpecker - a bird not seen in 60 years and thought to be extinct - the giant earthworm Sanchez-de Leon found last year already has been consigned to a jar of formaldehyde.

"Realistically, the giant Palouse earthworm is a lot less charismatic than a giant woodpecker," said James "Ding" Johnson, head of the University of Idaho's Department of Plant, Soil and Entomology Sciences. Johnson, himself, found several of the giant earthworms during graduate studies in the late 1980s.

There is urgency to find more Palouse giants because earthworms play an important part in the health of soil and plants, the scientists said.

"Earthworms are considered nature's tillers. They're extremely important for soil quality and from the standpoint of managing to grow plants better," said Ann Kennedy, a Washington State University soil scientist and veteran of several unsuccessful giant Palouse earthworm expeditions.

"It's one of a whole group of macrofauna that burrow and move organic matter from the surface down to deeper depths," Kennedy said. "It's amazing how far down you can find matter."

Sanchez-de Leon spent two years digging in WSU's Smoot Hill Ecological Reserve north of Pullman, about 65 miles south of Spokane - where the giant earthworm had been found previously.

The 800-acre reserve is thought to be one of the last remaining segments of the 2 million-square-acre Palouse shrub-steppe prairie of north-central Idaho and southeastern Washington.

The Palouse region was formed from ashfalls from Cascade Mountain volcanic eruptions. The wind-blown loess is hundreds of feet deep in places and supports a carpet of wheat on rolling hillsides.

The Palouse-area scientists think the earthworm's length and feeding habits might contribute to its scarcity.

These earthworms don't regenerate when cut by plows and tillage disturbs the layer of surface vegetation where they eat, the scientists think.

Other factors could be changes to their native habitat, or competition from other species of earthworms brought West by settlers, the Idaho and WSU scientists said.

Because the giant worms may "hibernate" deep underground until surface conditions are just right, it is not known how many there are, Kennedy said.

"The historic records lack enough precision for us to know how common they were before the Palouse was tilled. There are early oral reports of seeing these giant worms," Johnson said.

Unlike the giant sand worms of "Dune," the science-fiction work made into a movie in 1984, or the man-eating underground dwellers of 1990s movie "Tremors," the giant Palouse worms appear to eat only vegetation and an occasional insect.

That lily scent the worms are reported to give off is thought to be a defense mechanism, Johnson and others said.

European worms, which were brought West by settlers, may have crowded out the native worms, Johnson said.

"We're not exactly sure why they're going extinct," Johnson said. "Apparently, the natives did not evolve with tillage, with the plants we've introduced. We've changed their ecosystem and introduced a competitor."

Kennedy said scientists from Idaho and Washington State - land grant universities eight miles apart in the heart of the Palouse - will continue to look for the giant worm that has proved to be as elusive as another Northwest legend.

"It is kind of like a Bigfoot thing, but that's OK," Kennedy said. "Lately, worms are the big thing. People used to think they were kind of icky and now there kind of neat to talk about."