Any member of the widely occurring lepidopteran family Lycaenidae.
Adults, sometimes known as gossamer-winged butterflies, are small and delicate, with a wingspan of 0.75–1.5 in. (18–38 mm). Blues are rapid fliers, and most species have iridescent wings. Larvae are short, broad, and sluglike. Some species secrete honeydew, a sweet by-product of digestion that attracts ants, which stroke the larvae with their legs to stimulate honeydew secretion.