The best advice is to ask, if possible. There is a good chance that the bride and groom will appreciate people being dressed formally and will tell you so. Or they will tell you not to.
On the other hand, I disagree with the advice that you can never wear black tie if the invitation doesn't specify it. I have been to many weddings where some of the guests were in black tie even though the invitation said nothing. They looked fine and not at all out of place - it was an evening wedding, which is by definition fairly formal. Unless you know the wedding is of the aggressively informal type, then while suits are the norm,d black-tie might be unusual but still perfectly within the dress code. On the other hand, except when I have checked beforehand, I have never worn black tie when the invitation didn't specify it.