09 March 2008

Life History of the Chestnut Angle

Life History of the Chestnut Angle (Odontoptilum angulatum angulatum)

Butterfly Biodata:
Genus: Odontoptilum de Niceville, 1890
Species: angulatum C. Felder, 1862
Subspecies: angulatum C.Felder, 1862
Wingspan of Adult Butterfly: 40mm
Caterpillar Host Plants: Commersonia bartramia, Talipariti tiliaceum (Sea Hibiscus)

Physical Description of Adult Butterfly:
The forewing termen is sinuous, and the hindwing prominently stepped at vein 7. The upperside is chestnut-brown with a complex, cryptic pattern, and has a crescentic hyaline spot in space 2, and a smaller spot above it near the base of space 3. Hindwing has elongated tornal cilia. The male possesses a tuft of white hairs on the fore coxae, and the female has a thick anal tuft on the abdomen.

Field Observations of Butterfly Behaviour: This species is rather rare in Singapore. The adults are usually found near its larval food plants, or when feeding along a muddy track or on bird droppings. In Singapore, it may be found in an urban bushland where Commersonia bartramia grows, or about trees of Hibiscus tiliacus in coastal wetland. They frequently fly rapidly in bright sunshine in open spaces within forests or bushland, and visit flowers for nectar. Other sighting locations include various parts of the Central Catchment Area. Early Stages:

Host plant : Commersonia bartramia

The eggs are laid singly on the leaf upperside. Each egg is white and almost spherical with a flattened base and vertical ridges. The diameter is about 0.9mm. After an egg is laid, the mother butterfly rubs the tip of her abdomen over it. In so doing, pale brown abdominal hairs are glued to the chorion, effectively concealing the egg.

Egg covered in hairs (left), with hairs lost (right)

Mature egg (left), empty egg shell (right)
It takes 7 days for the collected egg to hatch. The young caterpillar eats just enough of the shell to emerge, and has a length of about 2mm. It has the typical cylindrical shape for skipper caterpillars, and there are short setae arising from regular rows of tubercles. The head is bilobed and hairy. The length of these fine "facial" hairs increases with instars.

1st instar caterpillar, length: 2.5mm

Soon after, the young caterpillar constructs its first leaf shelter by making short, curved cuts at the edge of the leaf and turns a small flap. It rests within the flap and ventures out to eat on nearby leaf surface.

The 1st leaf shelter for the 1st instar caterpillar
In later instars, the Chestnut Angle caterpillars make sinuous cuts which avoid the main veins so that the leaf flap remains green. They eat through the leaf at various points between leaf veins on this flap and this results in numerous holes appearing on the leaf shelter. It is interesting to note that Chestnut Angle caterpillars ballistically eject their individual faecal pellets (frass) at great speeds.

2nd instar caterpillar, early in this stage, length: 4mm

After 4 days in 1st instar and reaching a length of about 3.5mm, the caterpillar moults to the next instar. The 2nd instar (and in later instar) caterpillar has its body covered with short hairs arising from numerous low tubercles.

2nd instar caterpillar, late in this stage, length: 5mm

The 2nd instar caterpillar reaches a length of about 5.5mm, and after 6 days in this stage, it moults again. The 3rd instar takes 10 days to complete with the length reaching 12-13mm. During this period, the body color is initially yellow with a green undertone, but as the caterpillar develops, the color changes gradually to creamy white.

3rd instar caterpillar, early in this stage, length: 6mm

3rd instar caterpillar, late in this stage, length: 10mm

The 4th instar takes about 7 days to complete with body length reaching 19-20mm. The facial hairs are now visibly long and prominent.

4th instar caterpillar, early in this stage, length: 14mm

A leaf shelter for a 4th instar caterpillar in the field
The final and 5th instar cat has rather long and dense hairs on its head, giving it a very bushy appearance. This stage takes about 10 days to complete with body length reaching 30mm.

5th instar caterpillar, late in this stage, length: 27mm

At the end of 5th instar, the body of the caterpillar shrinks in length. Soon it becomes dormant in its leaf shelter and enters the preparatory pupa phase which lasts for one day.

Preparatory pupa of Chestnut Angle

Pupation takes place within the leaf shelter. The pupa secures itself with its cremaster attached to a short transverse band, and with vertcal and oblique threads connecting the transverse band and dorsal point of the girdle to the shelter wall. The pupa has a short thorax, a rather long abdomen, a short rostrum and low projections behind the prothoracic spiracles. There is also a pair of small but distinct orange projections on the anterior part of the mesothorax. Its body appearance is mostly white with a light green undertone, and against this background there are black spots arranged in neat symmetrical layout. Length of pupae: 17-19mm.

Fresh pupa of Chestnut Angle

After 7 days, the pupa becomes darkened in color signaling the imminent emergence of the adult. The next day the adult butterfly emerges from the mature pupa.

Mature pupa of Chestnut Angle

A newly eclosed Chestnut Angle

A newly eclosed Chestnut Angle resting on the inner side of a plastic container, showing its underside

  • 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