Mature nests of the Neotropical myrmicine ant Blepharidatta conops are short blind vertical cylinders, in general excavated directly in the ground. Nurse workers hold the larvae in their mandibles while resting along the nest's walls. When nests are visited or inhabited by myrmecophiles and/or predators, especially Histeridae beetles (adults and larvae), ant workers hide their brood in the nest's subsidiary chamber, the entrance of which is then blocked by the peculiar phragmotic disk of the single ergatoid queen in the colony. The extremely modified head and anterior slope of the pronotum of the queen, that jointly form the almost circular frontal disk, represent a new kind of cryptic phragmosis in ants; exceptional modifications of these structures, which are covered with intricate sculpture, enables the queen to behave as a living gate to the brood chamber, yielding entering nestmates when tapped by them on the disk. Workers use fine grained debris to build a wall at the beginning of the brood's chamber, such that the entrance opening matches the diameter of the queen's frontal disk. Observations in several different Brazilian localities revealed that the queens' frontal disk bear unique locality-specific sculpturing patterns, possibly due to viscous population structures caused by the limited dispersal by virgin queens, whose wing buds never develop.