Zerg Overview, Old Blizzard Page

Psychology
I would be hard pressed to determine the full extent of the Zerg intelligence, but it is clear that they are a very cunning species, and they are capable of higher reasoning. Although they do not use technology that we know of, they demonstrate a clear understanding of it, and have been known to open airlocks and doorways in colonies that they have raided. As a group they also react intelligently to attacks and are adept at tactical combat. On an individual basis, though, the Zerg seem to be hardly more than savage animals with little or no concern for self-preservation.