I see, yes the first instinct is to think that perhaps a lemming could survive forever by constantly bumping into other lemmings. But that's not possible becaus

I see, yes the first instinct is to think that perhaps a lemming could survive forever by constantly bumping into other lemmings. But that's not possible because a lemming traveling in the same direction as the candidate will never bump into him, and traveling in the opposite direction the maximum survival time after the bump is the 30 seconds I mentioned - which I why I only considered 2 ants. I hadn't quite got to the conclusion that a bump and change is equivalent to no bump and no change though.