blue butterfly, any Plebeiinaeany member of the insect subfamily Plebeiinae of a group of insects in the widely distributed Lycaenidae family of common butterflies (order Lepidoptera). Adult lycaenids, sometimes known as gossamer-winged butterflies, Adults are small and delicate, with a wingspan of 18 to 38 mm (0.75 inch to 1.5 inches). They are rapid fliers and are usually distinguished by iridescent blue wings. The male’s forelegs are reduced, but the female’s forelegs are fully developed.

Lycaenid larvae Larvae are short, broad, and sluglike. Some species secrete honeydew, a sweet by-product of digestion that attracts ants. The ants stroke, or “milk,” the larva with their legs to stimulate honeydew secretion. The fragile adults of most blue species have brilliant blue wing surfaces, generally much darker in the females than in the males; a . A few species have white or brown coloration. The pigmy blue (species Brephidium exilis), the smallest blue, has a wingspan of less than 12 mm; the tailed blues (Everes) have a taillike extension on the hindwings. The European blue (Maculinea arion) spends its larval and pupal stages in an ant nest, emerging in the spring as an adult.