I've seen various people try multispecies ant set ups and most have not gone well. The most successful have a massive outworld. But, too often it just degenerates into an excuse to set up an "ant war" which ends up being cruel or wasteful.
So, here is the question. Let's say you have a 40 gallon aquarium outworld and you are going to connect various ant colonies to this outworld. What combination of colonies would lead to the most stable environment?
I think ants with differences in being nocturnal and daytimes species ... would help. Also ants with very different diets and sizes?