Yes, they are black ants. They use a small gap to go in there (I found it) and no I don't have a living terrarium.
I think I am going to move my snake. He was suppose to move into his new terrarium this weekend or next weekend anyway (He is to big for the old one. It's 80cm long and he is about 1m). It's a bit more stressful for me but I can have the new terrarium done this evening. I think this might be my best option. I'll also buy ant baits so it won't happen with the new terrarium as well.