Genus: Arhopala Biosduval, 1832
Species: amphimuta C & R Felder, 1860
Subspecies: amphimuta C & R Felder, 1860
Wingspan of Adult Butterfly: 38mm
Caterpillar Host Plants: Macarange bancana (Euphorbiaceae, common name: Common Mahang).
Physical Description of Adult Butterfly:
Above, the male is violet with narrow but regular dark borders; the female is pale purple with broader dark borders than the male. Underneath, for both sexes, the post-discal band on the forewing is slightly dislocated at vein 4, and the post-discal spots in spaces 5, 6 ,7 on the hindwing overlapping and their centres aligned. The spot in space 3 on the forewing is usually an oblique oval. There are tornal green scales in the tailless hindwings which are slightly toothed at the end of vein 2.
Field Observations of Butterfly Behaviour:
This species is relatively common in Singapore. Sightings of the adults largely occur in the Central Catchment Area and Bukit Timah Nature Reserve where its host plant, Macaraga bancana is present in relative abundance. Typically the adults perch with its wings closed, but in sunny weather, they have the inclination to open their wings fully to sunbathe.
The host plant Macaranga bancana has often been mistaken as M. triloba (click here for a related article). It is a small tree with hollow twigs inhabited by ants of the Cremastogaster genus and featuring large broad reddish brown stipules at leaf nodes. Leaves are 3-lobed with leaf base broadly rounded. The immature stages of Arhopala amphimuta feed on the young leaves of M. bancana and has a symbiotic relationship with the inhabitant ants. When not feeding, the caterpillars in all instars have the habit of resting on the leaf underside, typically next to the adjoining main ribs at the leaf base.
Host plant: Macaranga bancana. A far view of its foliage.
Host plant: Macaranga bancana. Close-up view of its stem, showing broad and reddish brown stipules and the inhabitant ants.
A mother Arhopala amphimuta laying egg, during and immediate after the oviposition.
The egg is laid singly on the surface of a young leaf of the host plant. Each egg is about 1-1.1mm in diameter, white in color, depressed dome-shaped and feature many small broad-based spikes.
Two views of an egg of Arhopala amphimuta.
A mature egg with part of the chorion eaten away.
It takes 3-3.5 days for the egg to hatch. The newly hatched has a length of about 1.5mm and has a whitish coloration. It has a rather flattened woodlouse appearance with a large semicircular first thoracic segment. The large prothoracic shield is coloured as per the body base color. This onisform appearance remains as the caterpillar grows through the instars but becoming less flattened in later instars. The body also carries long lateral hairs and short dorsal hairs. As it grows, the body color becomes yellowish green.
Two views of a 1st instar caterpillar, newly hatched, length: 1.5mm
1st instar caterpillar, length: 2mm.
Two 1st instar caterpillars, one in early stage (left) and one in late stage (right) of this instar.
After 3-4 days of growth, and reaching a length of about 3mm, the caterpillar moults to the next instar. The 2nd instar caterpillar is yellowish green to green in body colour and has moderatlely long lateral hairs. The dorsum is somewhat more raised in this instar than the earlier instar. The dorsal nectary organ (DNO) and the tentacular organs (TOs) are present now, but they are still too small to be easily distinguisable. The 2nd instar caterpillar reaches a length of about 5mm, and after about 3-4 days in this stage, it moults again.
The same caterpillar. Top: in late 1st instar stage; Bottom: newly moulted to the 2nd instar.
2nd instar caterpillar, length: 4mm.
The 3rd instar caterpillar resembles the 2nd instar caterpillar closely. The body colour is yellowish green initially and for some specimens this remains so for the entire instar but others take on a pale reddish brown coloration on the lateral area of the body surface. The row of whitish spiracles now stand out against the darker body base colour. The 3rd instar takes about 3-4 days to complete with the body length reaching about 8-9mm.
Two 3rd instar caterpillars. Top: newly moulted, 5mm. Bottom: 6.5mm.
Two 3rd instar caterpillars resting against the main ribs at the leaf base.
The 4th instar caterpillar has similar appearance as in the 3rd instar. The intensity and extent of the reddish coloration on the body surface vary from specimen to specimen as depicted in the following series of three pictures. Now the DNO and TOs are all easily discernible. The 4th instar takes about 3-4 days to complete with the body length reaching up to 12-13mm.
Two views of a 4th instar caterpillar, length: 9mm.
Two views of another 4th instar caterpillar, with lesser intensity of reddish brown coloration, length: 9mm.
Two views of another 4th instar caterpillar, with greater intensity of reddish brown coloration, length: 11.5mm
The 5th instar caterpillar has similar body markings and variation of body colour as in the early two instars. With the increased body mass, the caterpillar has a less flattened body shape. In the field, these final instar caterpillars can be found resting against the reddish brown stipules on the stem.
Two views of a 5th instar caterpillar, late in this stage, length: 18mm.
The nectary organs of a 5th instar caterpillar. Dorsal nectary organ (DNO) on the 7th abdominal segment and the tentacular organs (TOs) on the 8th abdominal segment.
Two views of a 5th instar caterpillar being attended by ants which are particularly interested in the dorsal nectary organ (left side of the picture).
After about 7 days of feeding and reaching up to a length of 20mm, the caterpillar slows down and stops food intake for about 1 day. During this time, its body length gradually shortened. In the field, the caterpillar has been observed to choose the spot next to stipules as its pupation site. In a home breeding environment, the caterpillar chooses the gaps or space between leaf blades when leaf litter is offered.
A late 5th instar caterpillar resting against the reddish brown stipule in the field.
A pre-pupa of Arhopala amphimuta.
The pre-pupa caterpillar prepares for pupation by spinning a silk girdle and a silk pad to which it attaches itself via cremastral hooks. After 1 day as a pre-pupa, pupation takes place. The pupa, with a length of 13-14mm, has a shape typical of a Lycaenid species, and has a somewhat produced anal segment. It is mostly yellowish brown in coloration with dark brown patches in the wing cases and in mid body segments.
Two views of a pupa, length: 13mm
Eight days later, the pupa becomes darken especially in the thorax and wing cases, signalling that the pupal stage is coming to an end. The next day, the adult butterfly emerges.
Two views of a mature pupa.
A newly eclosed Arhopala amphimuta. Note the aberrated spots on the hindwings.
A 5th instar caterpillar being attended by ants in the field.
- [C&P4] The Butterflies of The Malay Peninsula, A.S. Corbet and H.M. Pendlebury, 4th Edition, The Malayan Nature Society.
- Butterflies of Thailand, Pisuth Ek-Amnuay, 1st Edition, 2006
- Immature stages and biology of Bornean Arhopala butterflies feeding on myrmecophytic Macaranga, T. Okubo, M. Yago and T. Itioka, Trans. Lepid. Soc. Japan, 60(1), pp.37-51, 2009
Text by Horace Tan, Photos by Henry Koh, Mark Wong, Anthony Wong, Federick Ho, Sunny Chir and Horace Tan