An attack by wolves upon civilized folk happens rarely, often only in times of desperation and even then only when the wolves have the advantage of numbers. This can change during a Blight. When darkspawn rise onto the surface their presence dramatically alters the savage nature of normal beasts.
—From Codex entry: Wolf

In Blights past, as the corruption of the darkspawn spread through the wilder areas of Thedas, it would infect the animals found there, and the more powerful of them would survive and be transformed into a more vicious and dangerous beast. A blight wolf is one such example, a kind of ghoul, mad with the pain of its infection. Only through the overriding command of the darkspawn does it still retain some semblance of its pack instincts. Blight wolves are always found in large groups and will tend to overwhelm a single target if they can, using their numbers to their advantage. It is fortunate that these creatures rarely survive their corruption for long.
--From Codex entry: Wolf