The butterfly is 21 to 29 mm (0.83 to 1.14 in) wide with wings outstretched and slightly shorter in length.

[6] Eastern tailed-blue larvae feed on various legumes and are known to secrete a substance which is favored by some ant species.

The Great Plains form a habitat boundary between the eastern and the much less common but similar western tailed-blue butterfly.

The central section of California and portions of the states of Oregon and Washington also has eastern tailed blues, which likely adapted to the habitat after being brought there inadvertently by man.

[5] The caterpillars feed on the seeds and flowers, and sometimes the leaves, of various legumes, including vetches and clover.