Leaf-cutter ant
In a mature leafcutter colony, ants are divided into castes, based mostly on size, that do different work.  Acromyrmex and Atta show a high degree of biological polymorphism, with four castes in established colonies - minims, minors, mediae and majors.  Majors are also known as soldiers.  Atta ants are more polymorphic than Acromyrmex, meaning there is comparatively less difference in size from the smallest to largest types of Acromymex.