Xordiah:
There are no aggressive critters on any of the maps playable on multiplayer right now and even non-aggresive for now the maps won't have a lot of critters. The goal is the keep the maps very easy to read and a lot of critters would cause confusion.
But nevertheless, it is still possible for the map making community to create maps and mods where you can do all kinds of things with critters. So scenarios like you have posted are quite possible and I'd certainly would like see you post some more ideas on how to integrate cirtters (aggressive or non-agressive) creatively in maps. ;) .