Minor soldiers can explode to damage and slow enemies down. Enemies are only knocked back when they are reduced to 0 HP by explosions.
Major soldiers can hunker down and permanently increase armor of nearby allies when they are fighting in their own nest. This ability is used continuously until the target is eliminated or has moved away.
Exploding
You can disable attacking to make minor soldiers only explode when they are attacked. You can disable exploding to make minor soldiers attack normally.
In real life, exploding ants are arboreal. In the game, they have to live underground due to map limitation.
In real life, exploding ants have 2 castes: minors and majors. In the game, the developers split the minors into workers and minor soldiers, probably to differentiate them from exploding termites.
In real life, major soldiers block nest entrances with their plug-shaped heads. Outside exploding ants must raise their gasters to be recognized as colony members and let in.