"Like the black wood-dogs, the Bushmen often in fits of savage frenzy destroy thrice as much as they can devour, trapping deer in wickerwork hedges, or pitfalls, and cutting the miserable animals in pieces, for mere thirst of blood."
After London, by Richard Jefferies
Black Wood Dogs
No. Enc.: 2d4 (4d4)
Movement: 120' (40')
Armor Class: 5
Hit Dice: 5
Attacks: 1 (Bite)
Vicious, blood-thirsty beasts who delight in tearing their prey to pieces for the sheer malice of it. Black Wood Dogs are highly destructive creatures, killing everything that they can with no consideration to what they can actually eat. They have no fixed territory, but rather once they deplete an area of all game they move on to find another spot to spoil. These feral canines are so mad with blood-lust that they cannot be tamed, only destroyed. They feel no pain, are immune to all forms of Fear, and will attack anything, including the undead, whom they regard as something especially toothsome.
What sets these creatures apart from wild dogs or dire wolves is that they never sleep, never stop moving, and are always on the hunt after fresh prey.
In most cases Black Wood Dogs prefer to eat other wild dogs, coyotes, dire wolves and the like, but from time to time a particularly powerful or vicious outsider will be allowed to run with a pack and sometimes they will inter-breed, though any pups produced by such liaisons tend to get devoured or abandoned while extremely young, almost always in the Spring. Low Land Farmers prize these pups greatly, and if treated well and trained properly, they become very loyal and stalwart guard and fighting dogs who are absolutely fearless in the darkest part of winter and who won't turn tail when confronted by mobs of biters or worse.
Too bad they can't be bred in the Low Lands. They too become sterile or distorted, producing unviable deformities or worse if they come to adulthood in the Low Lands due to the lingering effects of ancient weapons. Perhaps an enterprising family or two might relocate to one of the smaller plateaus in the East where they can raise more of these dogs free from the Low Land taint.
Being practical sorts, certain others among the Low Land farmers have recently discovered that Black Wood Dogs are resistant to the effects of Black Smoke, and that their hides retain this resistance when treated with lime to make stout cloaks...
Source: After London by Robert Jefferies, with a bit of a nod to Jack London.