After struggling for decades against an orange-toothed rodent that is eating the state's marshes, authorities in Maryland have claimed their first major victory over the nutria.

The animals, which are blamed for thousands of acres of vanished wetland across the state, have been eliminated from their former stronghold in Blackwater National Wildlife Refuge, officials said.

All it took was two years, $2 million and 15 trappers working in chest-deep muck here on the Eastern Shore. In all, about 8,300 nutria were killed during the eradication, which officials said was planned like a military campaign, using Global Positioning System equipment.

Although nutria remain in the state, Maryland is being lauded as a rare success story in the government's fight against the pest, which has colonized states from the Chesapeake Bay to Oregon.

"We proved it can be done," said Jonathan McKnight, an official with the Maryland Department of Natural Resources.

The Blackwater refuge originally contained about 13,000 acres of marshland, situated near the Chesapeake in Dorchester County. Nutria were introduced there when a few of the South American animals either escaped or were released from a federal fur research project in 1943.

For the nutria, which resemble waddling beavers with naked tails, the area turned out to be a garden spot. There were huge expanses of a marsh plant they love, called three-square bulrush.

For the bulrush, and the numerous species of birds, fish and mammals that lived in the bulrush marshes, the news was not so good. Nutria act like a "mammalian lawn mower," in the words of scientist Robert A. Thomas, a professor at Loyola University in New Orleans -- eating the plants, roots and all, and leaving huge stretches of bare mud.

Without roots to hold it, in many places the mud simply washed away. About half of the refuge's marshland, a crucial pollution filter that scientists call the "kidneys" of the Chesapeake, had become open water by the 1990s.

In monetary terms, nutria cause about $2.8 million worth of economic damage annually by reducing opportunities for hunting, fishing and hiking, according to a report by the Department of Natural Resources.

Aiming to reduce this damage, authorities first offered rewards to trappers who caught nutria: $1.50 apiece.

But there was a flaw. When nutria became difficult to find, trappers decided the rodent wasn't worth their time. Any remaining animals -- blessed with an ability to produce more than 10 young in a year -- would then quickly repopulate.

"It's sort of like a whack-a-mole game," said Steve Kendrot, an official with the U.S. Department of Agriculture who was in charge of Blackwater's trapping efforts.

Government officials also tried to make nutria into a dinner-table delicacy. That, too, failed: They found that people who will eat nutria are pretty much the same people who eat muskrat -- not much of a mass market.

"There's just not a lot of people out there who can stomach them," said Dan Murphy of the Fish and Wildlife Service's Chesapeake office.

Including him: "I don't eat rat," Murphy said.

The idea behind the recent eradication effort was to use full-time trappers, paid by the hour and not by the nutria. The trappers would act like a conquering army, slowly taking territory in a west-to-east march that was guided by GBS equipment.

In the summer, the trappers had to fend off mosquitoes and biting greenhead flies. There were also spiders and the danger of the occasional bite from a nutria's inch-long orange buckteeth.

Winter in the marsh, while often frigid, turned out to be the easy season. Once the water froze, the nutria couldn't swim away, and trappers could shoot them by the dozens on the ice.

"There's really about two months of the year when this is a pleasant occupation," Kendrot said.

This September, the anti-nutria team got the news they were waiting for: Surveys showed they had effectively cleared the animals from more than 35,000 acres in and around Blackwater.

As it turned out, the nutria death toll had been much lower than they expected, since early speculation was that 50,000 "nutes" were in the refuge. Scientists say the rest were killed by recent cold winters or by a decline in food, as so much of the marsh already was eaten.

With the nutria gone, the marsh is starting to look the way it did 70 years ago, officials said.

Yesterday, Murphy looked out over a bulrush marsh that was moving from mangy patches to thick, full growth.

"We saved it," he said.

Or at least part of it. The plan is for the Army Corps of Engineers to layer new dirt on some of the heavily eroded areas and replant it with marsh grasses.

Officials in Maryland said they hope the success achieved at Blackwater can be a model for the roughly 16 other states that have nutria problems.

One of them is Virginia, which has a small population south of Virginia Beach.

But in Louisiana, the only state with a bigger nutria population than Maryland's, authorities said they doubted whether a similar eradication was possible there. Millions of nutria are in that swampy state, and trappers routinely match the catch at Blackwater, about 8,300, in a couple of days.

In Maryland, authorities say they want to slowly expand their nutria-free zone to include the rest of the Eastern Shore, where tens of thousands more nutria lurk between the Chesapeake Bay Bridge and Ocean City.

Authorities also want to make sure that nutria can't sneak back in to Blackwater from neighboring areas. The whole effort will require millions more in funding and many more trappers, officials said.

"It was a major battle that has, for the most part, been won," said Jacoby Carter, a national expert on nutria for the U.S. Geological Survey. "But you've got to worry about the guerrilla warfare."

Nutria ate through about half of the marshland at the Blackwater National Wildlife Refuge, and the animals remain elsewhere in Maryland.Dan Murphy of the Fish and Wildlife Service looks over marshland that he says was saved by the elimination of nutria.A nutria at Stuart Park in Roseburg, Ore., flashes his orange-toothed smile.