Teratology in arthropods is widely reported, but the mechanisms leading to abnormal development are under-studied. This study focuses on a teratological case discovered during dissection, in which a male of the tawny crazy ant (Nylanderia fulva) exhibited genital duplication. Using nano-computed tomography, I generated three-dimensional models of the genital capsule to describe which structures were duplicated. The left side of the genital capsule appeared as normal, but the right side exhibited anomalies such as two additional gonostyles (parameres), an extra gonossiculus (digitus) on the volsella, and an additional volsella-like growth bearing peg-like denticles. This growth emerged between the mediad extra gonostyle and the penisvalva.