The Vampiric Wolf is a rare and dangerous variety of wolf in Baldur's Gate. This wolf can only be harmed by magical means, and it steals health from its targets with each point of damage dealt while potentially paralyzing them; Held if failing a Save vs. Death. As their name implies, they are undead and can likely be turned by clerics.
A good way to judge your party's ability to deal with a vampiric wolf is to watch its current health state through the tooltip. If it frequently reads "uninjured," you are likely not dealing enough damage to it quickly enough to defeat it.