Basically, there is a cave where worms are in Storm Peaks. (coords 47,55)

Well there are Worgs there that killed by the Worms, this is important because they spawn in a pair.

Once you kill the worms the spawn rate of the Worgs is totally insane. After a couple of minutes, it becomes an instant respawn between the four spots.

So you just run around the begging of the cave (as shown in the screenshot) and never run out of mobs, and besides Borean Leather, they do drop Artic Fur as well.

Here are the 4 locations:


I guess it would also be an awesome place for grinding too since you will experience no downtime between mobs.