These things spawn in tight groups of 5 around the grimling chief's hut as part of the Hollowshade War event. They will summon you as soon as they take any damage, so beware, although you may be 20, 30 levels higher they can and will kill you if you're not careful.
Another note: They backstab and proc a poison dot on you. If your class can slow I highly recommend you slow all five of them before you start killing them, and remember to keep facing them.
Edited, Wed Dec 15 10:42:14 2004