Castalius rosimon, the common Pierrot, is a small butterfly found in India that belongs to the lycaenids, or blues family. Distribution The species is found in Sri Lanka, India, Myanmar; Tenasserim, extending into the Malayan subregion. In the Indonesian archipelago the butterfly occurs in north-eastern Sumatra, Kalimantan, eastern Java, Bali, Bangka, Timor, Wetar, Kissar, Sumbawa and Sulawesi. In India the butterfly is found south of the outer ranges of the Himalayas, except in desert tracts; east India; the north-west Himalayas; Assam. The butterfly is also found in the Andaman Islands and the southern Nicobar Islands. Description Male The upperside of its wings is mainly white. Forewing has the costa, apex and termen edged with black, the edging much broader on apex and termen; base outwards for a short distance more or less densely overlaid. with metallic blue scales which cover and make indistinct a large basal outwardly clavate (club-shaped) black spot; a transverse black oval spot on the discocellulars touching the black edging on the costa; an oblique irregular line of four quadrate black spots beyond, the upper spot coalesced with the black on the costal border, the next spot below shifted outwards out of line, touching, as does also the lowest spot, the terminal black edging; posterior to this is a quadrate black spot in the apical half of interspace 2, and placed obliquely outwards from 1b coalescent with the terminal black border, another similar spot in interspace 1. Individuals of this species have been reported to exhibit seasonal colour variations and melanic aberrations that shows a similar pigmentation pattern. Hindwing: three basal black somewhat coalescent spots overlaid with metallic blue scaling; the costal margin above the subcostal vein and vein 7 black; this colour filling also the base of interspace 6, where in some specimens it is divided into a basal portion with a spot beyond; a postdiscal curved transverse black band followed by a subterminal transverse series of black spots, each spot edged inwardly and outwardly by very slender lunules of the white ground colour; on the inner side of the postdiscal band posteriorly is a broken line of four black generally coalescent spots two and two, the two upper often touching the postdiscal band. Underside primarily white. Forewing has a long oblique black band from base outwards to the costa; below it and obliquely placed an irregular black somewhat conical mark; following these are two outwardly