31 March 2012

Life History of the Malayan Snow Flat

Life History of the Malayan Snow Flat (Tagiades calligana)


Butterfly Biodata:
Genus: Tagiades
Hübner, 1819
Species: calligana Butler, 1879
Wingspan of Adult Butterfly: 36-40mm
Caterpillar Local Host Plant:
Dioscorea pyrifolia (Dioscoreaceae).

A Malayan Snow Flat displaying its wing underside.

A male Malayan Snow Flat resting on the side of a plastic container, giving us a view of its underside.

A newly eclosed male Malayan Snow Flat.

Physical Description of Adult Butterfly:
Above, the wings are dark brown. On the forewing, there is a white hyaline spot in each of spaces 3,4,5,6,7,8 and 11.  The forewing cell features an elongate upper spot, and in some specimens, a smaller lower spot. Additionally, the female has one spot in space 2. On the hindwing, there is a large white tornal area  with its inner edge reaching vein 6. In this whitened area,  there are black marginal spots at the end of veins 1b, 2 3 and 4, with the one at  vein 1b rather faint and even absent in some specimens. There are additional black post-discal spots in spaces 5 and 6, lying at the edge of the whitened area.   Underneath, the wings are similarly marked as per above but with the  whitened area on the hindwing  extended to the basal area, and with the marginal spot at vein 1b much larger and prominent than that on the upperside.

A newly eclosed female  Malayan Snow Flat.

A female Malayan Snow Flat  resting on the side of a plastic container.

Field Observations of Butterfly Behaviour:  
This species is moderately rare in Singapore and its distribution is restricted to the forested areas of the  Central Catchment and Bukit Timah nature reserves. The adults are strong flyers  and are more active in the cooler hours of the day.  As is the case for the other Tagiades species, the adults have the habit of perching on the underside of a leaf between flights, and with its wings opened flat.

A Malayan Snow Flat perching on the underside of a leaf.




Early Stages:
To date only one local host plant, Dioscorea pyrifolia, has been recorded for the Malayan Snow Flat. This plant can be found growing at a few sites within the local nature reserves. It is possible  that  one or more of other Dioscorea spp. present in the nature reserves is/are the larval host for  the Malayan Snow Flat. Further field observations are needed to ascertain this. The caterpillars of the Malayan Snow Flat feed on  leaves of the host plant. When not  feeding, the caterpillars seek  safety and concealment in a leaf shelter formed  by cutting and folding a leaf fragment along the edge of the leaf. 

Local host plant: Dioscorea pyrifolia.

A partially eaten leaf of the host plant with a leaf shelter.

The eggs of the Malayan Snow Flat are laid singly on the petiole of a young leaf  of the host plant. The whitish egg is hemispherical  with surface marked with longitudinal ridges running from the pole to the rim of the base. The egg  is well concealed in a mass of black setae deposited by the mother butterfly.  Each egg has a diameter of about 0.9-1mm.

Two views of an egg of the Malayan Snow Flat.

Two views of a mature egg of the Malayan Snow Flat. Note the polar portion of the egg shell has already been nibbled away.

The egg takes about 3-4 days to hatch. The young caterpillar emerges by eating away the polar  part of the egg shell. The rest of the egg shell is not eaten by the newly hatched which is about 1.8-1.9mm in length. The pale yellowish  body is roughly cylindrical in shape and the head capsule is black in color.

Two views of a  newly hatched caterpillar, length: 1.9mm.

The newly hatched makes its way to the leaf edge to  construct its very first  leaf shelter right away.  It ventures out of the shelter from time to time to feed on the leaf lamina in the vicinity. As the caterpillar grows, the body assumes a strong green to dark green undertone.   After reaching about 3.5mm in about 3 days, the caterpillar moults to the 2nd instar.

Two views of a  1st instar caterpillar, late in this stage, length: 3.5mm.

The body of the 2nd instar caterpillar is pale  whitish with a green undertone.  The head is black and broadened sideways to two short  tips at the upper end.  The  surface of  the body is dotted with  numerous tiny whitish speckles. This instar lasts about 3  days with the body length reaching about 6.5-7mm.

Two views of a 2nd instar caterpillar,  length: 6.5mm.

A 2nd instar caterpillar mid-way through the construction of its leaf shelter.

The 3rd instar caterpillar closely resembles the 2nd instar caterpillar. The head capsule is still black but broader sideways and with the two raised tips more angled and prominent. The tiny speckles  are whitish to yellowish. This instar takes about 3-4 days to complete with body length reaching about 12mm.

Two views of a 3rd instar caterpillar,  length: 9.5mm.

A late 3rd instar caterpillar, dormant prior to its moult.

The 4th instar caterpillar is little changed  from the  3rd instar in both body markings and coloration.   This instar lasts about 4 days with body length reaching about 21mm.

Two views of a 4th instar caterpillar, length: 19.5mm.

Two views of a late 4th instar caterpillar, dormant prior to its moult.

The 5th instar caterpillar has similar body markings as in the 4th instar but the colour of its head changed to a pale shade of reddish brown. The body markings become increasing yellowish as growth proceeds in this instar. The 5th instar lasts for about 8-8.5 days, and the body length reaches up to 30mm.

A newly moulted  5th instar caterpillar, its head capsule still "uncoloured".

Two views of a 5th instar caterpillar, early  in this stage, length: 21mm.

Two views of a 5th instar caterpillar, later in this stage, length:30mm.

On the last day of 5th instar, the body decolorises  to a very pale shade of yellowish green. The caterpillar ceases feeding and stations within its leaf shelter. The pre-pupatory larva prepares for the pupal phase with a series of silk construction work with the main pieces being a silk girdle across the dorsum of its early abdominal segments, and a short and thickened transverse silk band on the substrate at  its posterior end. Both the dorsal point of the girdle and the transverse band are further secured by vertical/oblique threads to the inner wall of the shelter. Soon the pre-pupatory larva becomes dormant in its leaf shelter. Pupation takes place about 0.5-1 day later.

The pre-pupa and the fresh pupa of a brown form  Malayan Snow Flat caterpillar.

The girdled pupa is secured  with its cremaster attached to the short transverse band on the substrate. It has a short thorax, a rather long abdomen, a pointed rostrum and two small ear-like appendages at the leading edge of the mesothorax. The body is pale beige brown with two large triangular white patches on the side of the mesothorax and first three abdominal segments.  Length of pupae: 20-21mm.

Two views of a pupa of the Malayan Snow Flat.

Frontal and side views of the anterior of a  pupa of the Malayan Snow Flat.

After about 7 days of pupal development, the pupal turns dark. The following day, the adult butterfly emerges from the pupal case.

Two views of a mature pupa of the Malayan Snow Flat.

References:
  • 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.
Text by Horace Tan, Photos by Tan Ben Jin, Sunny Chir and Horace Tan

1 comment:

John said...

This is a very beautiful and interesting research
The most educating one i have read today!




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