The ant colony is a life unit for ants consisting of different female castes and males. Workers are mainly responsible for feeding and defence, while the queen and males are mainly responsible for colony continuity. The queen is also rarely active away from the nest, let alone preserved as a fossil with other workers. Male ants develop from unfertilised ant eggs, and the vast morphological differences make identification of males so difficult and often neglected in fossils that they are known as the 'forgotten caste'. In this study, we introduce tGerontoformica priapos sp.n. based on a male specimen and report for the first time the discovery of an ant colony specimen that includes both morphologically differentiated queen and worker castes of stem ants in a single piece of mid-Cretaceous Kachin amber. The type specimen of tGeront-oformica priapos sp.n. features well-preserved genitalia and wing venation, filling a critical gap in our comparative studies of sexual morphological differentiation in stem-group ants. Additionally, the discovery of this ant colony provides new insights into the morphological differentiation among different castes of tGerontoformica females. To facilitate future research, we also provide detailed morphological diagrams for the various castes and sexes of tGerontoformica.