MORPHOLOGY
External characteristics
Male
Forewings: Forewing upperside black, large orange area in frontal half; underside black with greenish submarginal and median spots and in cell. Hindwings Hindwing upperside almost completely orange, with some golden yellow spots and patches, surrounded by black along margin; underside green turning to yellowish towards margin , veins broadly outlined in black; large black median spots,followed bij orange-yellow submarginal spots, yellow areas in basal part of spaces 6 and 7, and in upper part of cell. See also under Geographic variation.
Female
Forewing, upperside black with whitish submarginal and median spots, and elongate irregular patch in cell; underside similar. Hindwing, upperside black with prominent dirty yellow squarish submarginal spots and arrow-like median spots; underside similar. See also under Variation.
Subspecies and variation
Two subspecies are recognized, which are remarkably different. The description above relates to ssp. croesus. Male of ssp. lydius with upperside hindwing golden orange-yellow in frontal part, rest of wing orange dusted brown, round black spots in spaces 4-6; underside of both wings green and orange much more extensive, veins broadly outlined in black. Female of ssp. lydius has forewing and hindwing with pale areas much extended so that the black color is mainly restricted to the margins, veins (broadly on forewing), a ziczac submarginal line on forewing and black semicircular spots on hindwing.
Similar species
The males cannot be mistaken for any other Ornithoptera species, since there are no other orange species. Both forms of female are unlike other Ornithoptera species.
source: Jan Moonen, peronal communication 2020