Male: The male is smaller than the female (wingspan 147-200 mm) and is predominantly black with large areas of iridescent blue/green colour. In both sexes, the head and thorax are black being distinctly red anteriad; the abdomen is bright yellow (2, 4, 6, 8); the upper forewing is elongated, black with a long, broad, green radial band, a broad, blue-green anal band fused at both ends with a narrower cubital band to enclose a large, black sex band. The lower part of the forewing is blue-green with more blue towards the anal region; there are black veins, a narrow margin and sub-apical streaks. The hindwing is elongated, with a black background, sub-marginal cell and wing margin. There is a broad, blue-green submarginal band, which is continued to the base along the costal and inner margins; blue-green anal cell; underside of the hindwing is yellow, with black veins narrowing at the margins. Males are sometimes confused with O. priamus (6, pp. 10-11).
Female: The females are predominantly dark brown with an average wingspan of 200mm (187-300), with the largest females coming from the remote Managalas Plateau. The female is often confused with O. priamus (2, 4, 6, 8).
The forewing is dark brown with relatively small, light submarginal and discal spots becoming smaller towards the apex. The hindwing is elongated, with a band of seven pale grey, yellow-powdered, wedge-shaped pale patches separated by broad black bands over the veins. All but the innermost cells contain brown discal spots, and all are more yellow on the upper hindwing.