VIGNOLS, France — High in the thick grass meadows of the southern French Alps, a modern parable of man and nature, sheep and wolf, is being written in a great quantity of blood.

With official encouragement, herders and farmers had hunted the gray wolf to extinction in France by the 1930s. Within a half-century, though, the animal had been made a protected species throughout Europe; the first wolves re-entered French territory from Italy in 1992, a small and delicate population at the outset. Much to the thrill of conservationists and European officials, they have thrived.

But to the exasperation of this region’s shepherds, who for generations have scaled these hills with the seasons, the species’ success has been due in no small part to the ample, easy pickings. Wolves have been slaughtering vast numbers of sheep here — at least 20,000 in just the past five years, according to an official count. The government has spent tens of millions of euros in efforts to stanch the attacks, but to little avail, and shepherds increasingly call the wolf an existential threat.

“They’re killing shepherding as I know it,” said Bernard Bruno, 47, who has lost at least a thousand sheep in recent years. The wolf’s return may symbolize environmental progress to some, said Mr. Bruno, a stout, blue-eyed man who has spent 25 summers alone here with his flock and a walking stick. But it has also imperiled “one of the last natural, ecological kinds of livestock farming,” he said.