I agree, Mike. I tried to slip in a fresh female into a colony once back when I didn't know any better. It was a blood bath within seconds. The colony females took after her and even the male joined in. I've never done that again.

I always set up my groups like you do, freshly weaned. That seems to work best and I've not had a male, or female for that matter, killed doing it this way. I figure they will breed when they are ready and while they are still maturing they can work out their social ranking system (and boy do they have one).