The Lycaenidae are the second-largest family of butterflies, with about 6000 species worldwide. They constitute about 40% of the known butterfly species.
The family is traditionally divided into the subfamilies of the blues (Polyommatinae), the coppers (Lycaeninae), the hairstreaks (Theclinae) and the harvesters (Miletinae); others include the Lipteninae, Liphyrinae, Curetinae and Poritiinae. A few authorities still include the family Riodinidae within the Lycaenidae. The monotypic former subfamily Styginae represented by Styx infernalis from the Peruvian Andes has been placed within the subfamily Euselasiinae of the family Riodinidae.
Adults are small, under 5 cm usually, and brightly coloured, sometimes with a metallic gloss. The male's forelegs are reduced in size and lack claws.
Larvae are often flattened rather than cylindrical, with glands that may produce secretions that attract and subdue ants. Their cuticles tend to be thickened. Some larva are capable of producing vibrations and low sounds that are transmitted through the substrates they inhabit. They use these sounds to communicate with ants.
Source: en.wikipedia.org/wiki/Lycaenidae - 04.10.2010
It is the same as with many butterflies: the Lycaenida looks clearly different on the lower side than on the upper side of the wings.