I introduced this tag because ACO is a well developed sub-field of swarm intelligence, so it deserves (IHMO) its own tag, like e.g. reinforcement learning deserves its own tag (compared to machine learning) on a website dedicated to AI.
I used ant-colony because it is shorter and there's no ambiguity in the field of AI. Furthermore, a lot of people do not refer to these algorithms as "ACO", but e.g. as "ant colony system" or just "ant colony algorithms". I would argue that ant-colony is a more general tag and expression.
Furthermore, several questions on ACO have already been asked on the website.