17 August 2008

The Life History of the Yamfly

Life History of the Yamfly (Loxura atymnus fuconius)

Butterfly Biodata:
Genus: Loxura Horsfield, 1829
Species: atymnus Stoll, 1780
fuconius Fruhstorfer, 1912
Wingspan of Adult Butterfly: 35mm
Caterpillar Local Host Plants:
Smilax bracteata (Smilacaceae)

Physical Description of Adult Butterfly:
The upperside of both sexes is reddish orange, with a neat black apical border on the forewing. The underside is yellowish buff with a somewhat obscure post-discal fascia. The female has its tornal area of the hindwing dark-dusted. The antennae are short and the palpi are unusually long and protruding, a feature easy to pick in close-up pictures. Both sexes have rather long white-tipped hindwing tails.

A female Yamfly sunbathing in mid-day sun, showing us its upperside

Field Observations of Butterfly Behaviour:
Locally, this species is uncommon, and the adult is usually encountered singly. Typical encounters take place in bright sunlit spots with the adult sunbathing or flitting from perch to perch in the vicinity of its local host plant. It has a wide distribution with sightings recorded in many locations such as the Central Catchment Area, Bukit Timah Nature Reserve, Southern Ridges and even abandoned farmland in the western part of Singapore.

Early Stages:
In the region the recorded host plants of the Yamfly include various Dioscorea (Yam) and Smilax species. Thus far, Smilax bracteata is the only local host plant recorded. This native plant is a woody climber with long, coiling stipular tendrils and long, stout stems which are covered with bristles and stiff prickles. Leaves are ovate with a round base. This plant can be found in open country and forest edges in various parts of Singapore. It has been found to smoother native plants in nature reserves by growing over them and blocking out sunlight. As the name bracteata suggests, it has "shiny" young stems and leaves, and it is on these young stems that a mother Yamfly lays its eggs.

Host plant : Smilax bracteata, stem with mature leaves
climbing a fig tree

Young and fleshy shoot of Smilax bracteata.

A mother Yamfly laying eggs on the young shoot of Smilax bracteata

Eggs are laid on the young shoots of the host plant. It is not uncommon for a number of eggs to be found on the same shoot, however the eggs occur singly rather than in clusters. Each egg is white, circular and has a depressed micropylar area. The surface is covered with many tiny shallow pits which are barely visible to the naked eyes. Each egg has a diameter of about 0.9mm.

Left: fresh egg; right: mature egg showing part of the egg shell already eaten
by the soon-to-emerge caterpillar.

1st instar caterpillar, newly hatched, length:1.3mm

It takes 3 days for the egg to hatch. The young caterpillar consumes the upper portion of the egg shell to emerge. With a length of 1.2-1.3mm, it has a black head, a pale yellowish body decorated with long setae (hairs) dorsally and sub-spiracularly. The caterpillar assumes the typical woodlouse body shape as it grows in this instar which lasts about 2 days and sees the body length increased to about 3mm. The body color also changes gradually to darker shades of yellow, together with the presence of orange to red tinge. The caterpillar feeds by eating away the upper layer of the fleshy young shoot in almost all instars.

1st instar caterpillar, length: 2.3mm

1st instar caterpillar, ready to moult to the next stage, length: 3mm

The 2nd instar caterpillar has a
roughly diamond-shaped prothoracic shield in the same color as the rest of its body. The long setae are now gone. The anal plate has a rather prominent depression, roughly oblong in outline. Also discernible are faint yellowish markings on the side of a thin red or reddish brown dorsal band. The 2nd instar lasts for 3 days and reaches a length of about 6m to 7mm.

2nd instar caterpillar, early in this stage, length: 3.7mm

2nd instar caterpillar, late in this stage, length:6mm.

The 3rd instar caterpillar looks similar to the 2nd instar caterpillar, except for the greater size which has the body length reaching a maximum of around 9-10mm. After 2-3 days in this stage, the next moult takes place.

3rd instar caterpillar, length: 9mm

In the midst of the moult from 3rd to 4th instar

The 4th (and final) instar caterpillar initially resembles the 3rd instar caterpillar in the day prior to the moult. Over the next 2-3 days, the pink to red patches on the body gradually darken such that the dorsal markings are now more prominent with the greater contrast between the yellowish green and the darkish pink patches.

4th instar caterpillar, length: 19mm

The 4th instar lasts for 4 days and the body reaches a length of about 19-20mm. In the last day of this stage, the caterpillar ceases feeding, and its body shrinks in length. Soon it comes to rest on a spot on the young shoot, or a leaf or even a tendril and it becomes an immobile pre-pupa.
There the pre-pupatory caterpillar prepares for pupation by spinning a silk pad and a silk girdle to secure itself.

Two views of a pre-pupa of the Yamfly

The next day, after 12-13 days of larval growth, pupation finally takes place. The pupa is held via its cremaster and a silk girdle to the silk pad on the leaf surface. It is 13-14mm in length, mostly green with a relatively long abdominal section. Large dorsal markings of cryptic patterns in brown and white are present. The wing pads are whitish and stand out against the green base color of the pupa.

Two views of a fresh pupa of the Yamfly

Seven days later, the pupa becomes darkened in color signaling the imminent emergence of the adult. The orange patches on the forewing upperside becomes visible through the now transparent pupal skin. The next day the adult butterfly emerges from the mature pupa.

Two views of a mature pupa of the Yamfly showing the orange patch
on the forewing upperside

A newly eclosed Yamfly resting on a perch

A sun-facing Yamfly perching on a Smilax shoot


  • The Butterflies of The Malay Peninsula, A.S. Corbet and H.M. Pendlebury, 4th Edition, Malayan Nature Society.
  • Butterflies of Thailand, Pisuth Ek-Amnuay, 1st Edition, 2006
Text and Photos by Horace Tan