hm_black_forest addon - Headcrab Mod for Counter-Strike: Source

As a squad of combine soldiers, the players must annihilate a horde of +50 headcrabs who will constantly harras them until the king headcrabs make their entrances in the game. With help of their guns, special grenades and team works, they will have to defeat the whole horde but they should also be aware of not getting zombified by a headhumper !