The black rajah is a medium-sized butterfly with a 70 to 80 mm wingspan. Above, the butterfly is dark brownish black with greenish or white discal bands across both the wings. The band is broken into spots towards the apex of the forewing. The hindwing has two similar-sized tails at veins 2 and 4. These tails are longer in the females and more pointed in the males.
Male
The upper side is blackish olive-brown, palest basally. Forewing with a transverse discal recurved series of eight yellow spots increasing in size from near the costa, the upper spots mostly rounded, the lower spots being broad and irregularly quadrate with uneven exterior; also a yellowsubcostal spot between the lower subcostal veinlets and upper radial, and a smaller spot outside end of the cell above the upper median veinlet; a marginal lower row of minute yellow spots which are more or less obsolescent anteriorly. Hindwing with a transverse discal yellow irregular band, decreasing posteriorly; a submarginal row of small, yellow lunules, and a marginal row of small geminate spots, those at the anal angle being greenish-grey. The underside is lilac-grey, of a more or less pale or darker tint, but dullest at the base, and purplish-tinted externally. Both wings with white transverse discal markings as on upperside, but each inwardly-edged by a black line; the basal area crossed by irregular black slender lines. Forewing also with three basal black spots in the cell, a submarginal row of ochreous-yellow spots with posteriorly increasing black borders, and a marginal lower row of indistinct purplish-white lunules. Hindwing also with a discal more or less defined irregular row of black-edged purplish-white lunules, and a submarginal row of ochreous-yellow spots with blackish outer borders, followed by a marginal row of small, more or less ochreous-yellow or greenish-ochreous lunules surmounted by an indented black line and white speckles above, and broken lunate white spots below; the extreme margin and tails being blackish-edged."
Female
The upperside as in the male, with the markings somewhat larger. Underside as in the male." The body is dark olive-brown above; the collar, front and palpi are black above, spotted with white; the palpi, body beneath, and the legs are whitish; the fore tibiae are brown above; the antennae black and the eyes reddish."
Egg
Its egg is transparent yellow and spherical, with longitudinal ridges. It has a dark red uneven band around its upper half.
Caterpillar
The caterpillar is dark green with irregular rows of yellow tubercles. The caterpillar is cylindrical and may have a round white blotch on the seventh segment. The head is outcurved and has horns and spines. The pupa is short, dark green and it has a lateral longitudinal line which is marbled white.
The black rajah is generally a low-elevation butterfly and can be found at altitudes up to 1950 m ASL. The caterpillars generally feed on Fabaceae, such as tamarind Tamarindus indica. At least on Borneo but probably elsewhere too, adults do generally not visitcarrion or old fruit to drink liquids.
