In Ant Nation, the player helps a ant colony to survive against their enemies: vermin and spiders. From space. This does not manifest in their looks, just in some of their ranged attacks and the story cutscenes in which a mad professor introduces new problems.
From a gameplay perspective, this is a toned-down real-time strategy game. There are two kinds of ants to work with: collectors and fighters. The former collect food in the environment (which is required to extend the hive and get more ants) and open crates which start the missions. There the player has to solve different tasks (e.g. killing all enemies or destroying the enemy hive) within a time limit by using the fighters. Ants can also be divided in elementary groups (water, fire or poison) which helps then overcoming environmental obstacles. The control are indirect: the player selects a group and a target point. Then the ants move to this point and independently decide what to do; a possible result could be that they abort movement if they decide something else nearby is more important. Moving targets can't be marked. Sometimes the hive, which is always shown on the DS' upper screen, is hit by a catastrophe: then the player has to remove debris with the Stylus.
Additionally there is a two-player mode which is basically rock-paper-scissors with elemental proficiencies.