Marathyssa basalis is a species of insect belonging to the family Lycaenidae. It is commonly known as the Eastern Tailed-Blue butterfly. This small butterfly has a wingspan of about 1 inch and is characterized by its vibrant blue coloration on the upper side of its wings, while the underside is pale gray with orange spots. It is found in eastern North America and is known for its rapid flight and ability to adapt to a variety of habitats.