Ergatoid queens and intercastes in ants: Two distinct adult forms which look morphologically intermediate between workers and winged queens

Summary The term ergatogyne is used in ants to describe permanently-wingless female adults which are morphologically intermediate between workers and winged queens. This definition is ambiguous because there are two distinct categories of ergatogynes: ergatoid queens and intercastes. Both have an external appearance (ocelli and alitrunk structure) which combines traditional queen and worker characters, and thus can be confused if they both function as reproductives — however intercastes in most species cannot reproduce.Ergatoid queens have replaced winged queens in a substantial number of species. They are sometimes externally similar to conspecific workers, especially in various ponerine species which exhibit limited size dimorphism between castes. Ergatoid queens retain the specialized attributes of a reproductive caste, including larger ovaries, and they are always the functional egg-layers in a colony. In contrast, conspecific intercastes represent various graded stages in a series connecting workers and winged queens, and they occur together with the queens. These hybrid phenotypes result from deviations from the normal pattern of caste differentiation during larval development. Intercastes generally lack a spermatheca and have no reproductive function; however they can mate in a few leptothoracine ants, and then reproduce instead of winged queens in a proportion of colonies.