Why don't ants normally form super colony?

Answer 1

Most species of ants defend their nests against other ants, whether of the same species or not. As a rule they keep away from strange nests and can tell their own nest by the way it smells different from strange nests. If one colony does in fact invade a strange nest, there will usually be a fight with many ants being killed; when that happens one of the colonies might be wiped out, with the eggs and larvae being eaten by the victors or taken home as "slaves". In either case, no super colony results.

Sometimes because of inbreeding the different ant colonies smell so much alike that the smells do not set the ants fighting. When that happens ants move perfectly happily between colonies and a nest might include many queens. An example is when Argentine ants (the species Linepithema humile) invade a new country or an island because humans accidentally transported them. The result sometimes is that only one Argentine ant colony is imported and their young are so inbred that they form super colonies and kill all the local ants because the local ants are not inbred and so do not form super colonies and the Argentine ants outnumber them and kill them.