We describe diverse species of Lepidoptera in immature stages exhibiting a wide range of previously unreported collective behaviors. These behaviors include coordinated foraging, group defense, trail-marking, resting-site selection, and pupation and demonstrate high levels of synchronization among groups of a dozen up to hundreds of individuals. Our research encompassed twenty groups across ten Lepidoptera species, and employed field monitoring/observations and controlled experiments in the Peruvian Amazon and Karnataka. The behaviors observed are complex and metabolically expensive as they require interaction between many individuals and significant movement. For example, one group of 320 individuals performed a ~40 minute “milling” motion before hour-long foraging bouts involving synchronized processionary travel for ~25 meters (~500 body lengths). The prevalence of these behaviors across multiple taxa suggests they may confer a fitness advantage, leading to its repeated emergence in Lepidoptera. Notably, while individual behaviors such as movement patterns, feeding habits, and chronotypes are highly species-specific, group behaviors like self-organized synchronization and distributed foraging show remarkable conservation across taxa. Our observations expand our understanding of social complexity in insects and the evolution of collective behavior while potentially revealing novel strategies for pest management in ecologically and agriculturally important Lepidoptera species. Furthermore, these principles of self-organization may have broader applications in fields such as swarm robotics and collective decision-making algorithms.