White Wolves were a type of wolf native to the frozen lands in the north of Middle-earth. They were not normally seen in Eriador, but seem to have remained among the snows of the Forodwaith and perhaps beyond.
In the year T.A. 2911, one of the harshest winters in Middle-earth's history descended, the so-called Fell Winter. The ice and snow of the north came at least as far south as the Shire. With them came the White Wolves, invading Eriador and roaming as far as the Shire. The frozen Brandywine River meant that they were even able to cross into the Eastfarthing. This was the last time the Horn-call of Buckland was used before the War of the Ring, one hundred and seven years later.