25 May 2008

Life History of the Malayan Bush Brown

Life History of the Malayan Bush Brown (Mycalesis fusca fusca)
Butterfly Biodata: Genus: Mycalesis Hübner, 1818 Species: fusca C. & R. Felder, 1860 Subspecies: fusca C. & R. Felder, 1860 Wingspan of Adult Butterfly: 45mm Caterpillar Host Plant: Scleria bancana Physical Description of Adult Butterfly: Underneath, both wings are yellowish brown in ground colour, with two reddish/orangy brown longitudinal stripes crossing from the upper to lower edges, and a series of moderate to small ringed spots (ocelli) in the submarginal area. The post-discal area of the hindwing carries a reddish brown coloration. Above, the male is brown with obscure post-discal ocelli while the female is pale brown with more distinct post-discal ocelli. The female is typically larger in size. Field Observations of Butterfly Behaviour: This species is one of the less common of the Mycalesis genus in Singapore, and thanks to its more striking undersides, it is also one of the more distinctive members of this genus which typically features dull brown adults. Local sighting locations include the Central Catchment Nature Reserve and the Bukit Timah Nature Reserve. Individuals are usually encountered flying alongside forest trails or lurking in shady undergrowth in the vicinity of its host plant. As with other Satyrinae members, the adults fly in an erratic and jerky manner as their wings are closed for a relatively long period during flights. Early Stages: The host plant is a member of the Cyperaceae (Sedge) family, a grass-like herb with triangular stems and 3-ranked leaves with sheaths. This plant is rather common in the Nature Reserves and even along trails in the Southern Ridges. Host plant : Scleria bancana The eggs of the Malayan Bush Brown are laid singly on the grass leaf blade. Each egg is more or less spherical (about 1mm in diameter) and light translucent yellow. It appears to be smooth to the naked eyes, but faintly sculptured with a hexagonal reticulum when viewed with a more extreme close-up camera set-up. A fresh egg of Malayan Bush Brown The egg takes 4 days to mature. The young caterpillar pushes its way through the cracked egg shell, and then proceeds to eat up the egg shell almost entirely. It has a spindle-shaped body in light creamy yellow colour, and an initial body length of about 4mm. The body has rugose and ill defined segments. There is a pair of backward-pointing anal projections and a black head with a pair of short and rounded horns on the head. The young caterpillar eats the leaf blade along the edge. Caterpillars of all instars are observed to be sluggish in movement. They tend to rest lengthwise on the underside of a leaf during pauses between feeds. Mature egg with the head about to break through the shell Newly hatched 1st instar caterpillar, length: 4mm The first instar lasts 4 days with the body length increases to about 6mm before the inevitable moult. With the change of instar, the two cephalic on the head become pointed and the two anal projections longer and thus pronounced. The body colour is yellow with a green undertone. The head and body is also roughened by numerous minute tubercles, each with a single seta. Faint longitudinal lines are also distinguishable on the body. 2nd instar caterpillar, early in this stage, 6.5mm 2nd instar caterpillar, late in this stage, length: 10mm The 2nd instar lasts for 4 days with the body length reaches about 11mm before the next moult. The 3rd instar caterpillar mostly resembles the previous instar except for having longer anal projections and more prominent longitudinal lines on its body. This stage also takes 4 days to complete with body length reaching about 16mm. 3rd instar caterpillar, early in this stage, length: 11mm 3rd instar caterpillar, late in this stage, length: 13mm One obvious change in the 4th instar caterpillar is in the head where the "face" area has changed from dark brown to yellowish green while the forward-facing portions of the horns remaining dark brown. The 4th instar lasts about 5 days with body length reaching 22-23mm. 4th instar caterpillar, length: 16mm The next moult brings the caterpillar to its 5th and final instar. Now the "face" area of the head is pale yellow in colour and decorated with three pairs of curved brown lines. The body is dotted with several prominent black spots, and the longitudinal lines become more striking with alternating and varying shades of brown and green. In a period of 9 days, the body grows at a faster pace to a maximum length of about 40-42mm. 5th instar caterpillar, early in the stage, 30mm 5th instar caterpillar, late in this stage, length: 40mm Toward the end of 5th instar, the body gradually shrinks in length and becomes paler in colouration. Finally the caterpillar finds a spot on the underside of a leaf blade to secure itself at the anal end. The dormant pre-pupatory pose is complete once it has its body curved up and the head touches part of the body. Preparatory pupa of Malayan Bush Brown After one day as a pre-pupa, pupation takes place. The smooth pupa is light woody brown with faint brown markings. It is somewhat angular, with a dorsal keel on the thorax and ridges defining the dorsal wing margins. Length of pupae: 15-16mm. Fresh pupa of Malayan Bush Brown After 9 days of development, the pupa becomes darkened in color especially at the wing pads (corresponding to the dark brown uppersides of the forewings). The next day the eclosion event takes place with the adult butterfly emerges to start the next life cycle. Mature pupa of Malayan Bush Brown A newly eclosed Malayan Bush Brown


  • The Butterflies of The Malay Peninsula, A.S. Corbet and H.M. Pendlebury, 4th Edition, Malayan Nature Society.
  • The Butterflies of Hong Kong, M. Bascombe, G. Johnston, F. Bascombe, Princeton University Press 1999
Text and Photos by Horace Tan