Eastern Tailed-Blues are one of the smallest, commonest and longest-present butterfly species around here in Maryland. Last year, they were flying in September and this spring I started seeing them towards the end of April. I photographed these butterflies about a week ago. According to Glassberg (Butterflies Through Binoculars, the East), in warm weather they breed continuously. The pictures of a mating pair that I photographed last September are here.
These butterflies are in a group called the blues (family Lycaenidae, subfamily Polyommatinae). The famous novelist Vladimir Nabokov (1899-1977) was also an accomplished lepidopterist and for a while worked at Harvard University's Museum of Comparative Zoology. He specialized in the family Lycaenidae.