The origin of these wolves is unknown.
White Wolves were seldom ever seen in Eriador, and seemed to have been limited to the snows of the Forodwaith and perhaps beyond. In the year 2911 of the Third Age, the harshest winter in the history of Middle-earth, the ice and snow of the north came at least as far south as the Shire, and with them came packs of the White Wolves. They roamed Eriador as far south as the Shire. Taking advantage of the frozen Brandywine River, they were even able to cross into the Eastfarthing, causing much trouble. The Horn-call of Buckland was used to summon able Bucklanders to drive them out. This was the last time Horn-call was used before the War of the Ring, one hundred and seven years later. Since the Hobbits of the Eastfarthing and Buckland survived, the White Wolves were killed and driven out or retreated on their own.
Behind the Scenes Edit
In the Hobbit Film Trilogy, Azog the Defiler rode a white warg. The wolves from the book were changed into wargs from the movies, so one may speculate that Azog's ravenous steed was indeed a white wolf/warg.