The colony of ants has always been more important as a whole than as single individuals, if you put a group of ants together in a jar(I did this as a child), most of the time they will try to escape instead of fighting. But if you put a group of ants on another ant's nest, it will be a bloody fight
Were the ones in the jar from the same colony? Is so, this also ties nicely back to the point about inclusive fitness, where the ants will work together with its relatives (colony mates) because they share genes, so it's beneficial for them if the other ants also survive. But they don't share many genes with ants from other colonies, so they will have no problem with slaughtering them.
If you jar ants from several different colonies together, it becomes a bit more complex to explain why they work together :P Hehe