Abstract: Many extant species spin cocoons before their pupal stage, which can protect them from predators, pathogens, and fluctuant environmental factors in nests. However, owing to the scarcity of ant cocoon fossils, little is known about the origin and evolution of this behavior in Formicidae. Here, we describe two ant pupae specimens from Myanmar amber. The presence of cocoons in these Mesozoic fossils suggests the ancestral origin of spinning cocoon behavior; based on our phylogenetic analysis and ancestral state reconstruction, this behavior was secondarily lost at least six times in Formicidae, which could be ascribed to the transition of nesting and feeding habits, as well as the development of eusociality. Moreover, the first specimen preserved worker ants with empty cocoons simultaneously, indicating garbage removal or brood care behavior, which improves our understanding of their eusociality in the Cretaceous.