The eastern tailed-blue or eastern tailed blue (Cupido comyntas), also known as Everes comyntas, is a common butterfly of eastern North America. It is a small butterfly that is distinguished from other blues in its range by the small thin tail. Eastern tailed-blue larvae feed on various legumes and are known to secrete a substance which is favored by some ant species. The ant in turn protects the larva of the butterfly from other predators.