07 January 2012

Life History of the Malay Dartlet

Life History of the Malay Dartlet (Oriens paragola)

Butterfly Biodata:
Genus: Oriens Evans, 1932
Species: paragola 
de Nicéille, 1896
Wingspan of Adult Butterfly: 22-27mm
Caterpillar Local Host Plant: Ottochloa nodosa (Poaceae).

Physical Description of Adult Butterfly:

Above, both sexes are dark chocolate brown with amber-coloured post-discal bands on both fore- and hindwings, and amber-coloured cilia on the hindwing termen. The forewing band stretches from the dorssm to almost touching the costa, and is deeply excavate at vein 5. The lower cell spot fuses with this band at space 2. The hindwing post-discal band is shorter, stopping well short of the costa.   Underneath, the wings are dark brown  with  post-discal bands mirroring those on the uppersides. These bands are sharply defined and not edged by black spots (as is the case of the Oriens gola, the Common Dartlet).

Field Observations of Butterfly Behaviour:
This species was not listed by early researchers as extant in Singapore. It was  discovered about one year ago and added to the Singapore checklist as species #297. According to C&P4, the Malay Dartlet frequents  lowland forests. However, adult sightings in Singapore  have so far been very infrequent and only confined to one grassland adjacent  to a forested area. The species has a preference for perching in semi-shady areas, and visiting flowers in the grassland for nectar. Given that the larval host plant is a common grass species, there is a possibility that Malay Dartlet exists elsewhere in Singapore. Even if this is not so now, this species  has the potential of spreading beyond the currently known location.

Early Stages:
The host plant, Ottochloa nodosa, is a common grass species which can be found in many locations in Singapore and is utilized by several other common skipper spp. (Common Dartlet, Chestbut Bob, and one Caltoris sp.) as larval host plant. The caterpillars of the Malay Dartlet feed on leaves of this plant, and live in shelters made by joining edges of a grass  blade together with silk threads.

Host plant: Ottochloa nodosa.

A female Malay Dartlet resting between oviposition runs.

A female Malay Dartlet laying an egg on the underside of a grass blade.

The eggs are laid singly on the underside of a leaf of the host plant. Between each oviposition run, during which one or two eggs are laid on separate leaves, the mother butterfly has the habit of  perching on a sunny spot  to re-energise  This could go on for a few rounds before the mother decides to retire altogether.  Each tall hemispherical egg is milky white and is finely recticulated.  The base diameter is about 0.75mm.

An egg of the Malay Dartlet.

A maturing egg of the Malay Dartlet.

A mature egg with the young caterpillar already nibbled away the polar part of the egg shell.

It takes about 5 days for the egg to hatch. The young caterpillar eats just enough of the shell to emerge, and will devour the rest of the egg shell after emergence. The newly hatched has a length of about 1.7-1.8mm. Its has a cylindrical body shape, very short dorso-lateral and sub-spiracular setae and a tuff of long setae at the posterior end. The body is creamy white with a prominent black collar on the dorsum of the prothorax. The head capsule is entirely black.

A newly hatched 1st instar caterpillar in the process of nibbling away its egg shell.

Two views of a newly hatched 1st instar caterpillar, soon after devouring the egg shell.

The body color changes to pale yellowish green after a few feeding sessions on the leaf. The newly hatched constructs its leaf shelter near the tip of a grass blade soon after it is done with the egg shell. Between feedings on the nearby leaf lamina, the caterpillar retreats to its shelter for rest and security. By the time the caterpillar lies dormant in its shelter for the moult to the 2nd instar, its length has reached about 4-4.5mm. The 1st instar takes about 4-4.5 days to complete.

Two views of a 1st instar caterpillar, early in this stage, length: 2.4mm.

Two views of a 1st instar caterpillar, late in this stage, length: 4mm.

The 2nd instar caterpillar is again whitish, but appears to be yellowish green with its "stomach" contents showing through the translucent cuticle.  The anal plate still carries a few setae but these are not as long and prominent as in the 1st instar. Although the prothoracic collar is still present, it appears to lose lighter in its black coloration. The head capsule is still black in colour. This instar lasts about 3-4 days with the body length reaching about 6.5-7mm.

Two views of a 2nd instar caterpillar, early in this stage, length: 4.2mm.

Two views of a 2nd instar caterpillar, length: 5.2mm.

The 3nd instar caterpillar resembles the 2nd instar caterpillar closely in body markings except for the diminishing black prothoracic collar.  Two faint whitish dorso-lateral bands, first appears in the 2nd instar but less obvious, are now discernible. This instar lasts about 2-3 days with the body length reaching about 8.5-9mm.

A newly moulted 3rd instar caterpillar, the head capsule is yet to turn black.

Two views of a 3rd instar caterpillar,  length: 7.2mm.

Two views of a 3nd instar caterpillar, later in this stage. length: 8.2mm.

The 4th instar caterpillar resembles the 3rd instar caterpillar closely but with the black prothoracic collar almost completely  diminished. As in the earlier instars, the head capsule is completely black and there is no markings on the anal plate.  This penultimate instar lasts 3-4 days with the body length reaching up to about 15.5-16mm.

Two views of a 4th instar caterpillar, early in this stage, length: 12mm.

Two views of a 4th instar caterpillar, late in this stage, length: 15.8mm.

The 5th (and final) instar caterpillar loses the black coloration of its head capsule seen in the earlier instars. The head is  now pale neutral yellow to neutral green. The body colour has a strong tone of yellowish white, with two broad and whitish dorso-lateral bands and two narrow pale yellowish lateral bands.  This instar takes about 6-8 days to complete with the body length reaching up to about 24-25mm.

Two views of a  newly moulted 5th instar caterpillar.

Two views of a 5th instar caterpillar, late in this intar, length: 24mm.

Towards the end of the 5th instar, the the body of the caterpillar shortens and its base coloration changes to a translucent pale green. Tyipcally it picks the underside of a grass glade for its pupation site. It becomes dormant in this shallow leaf shelter and enters the prepupatory phase which lasts for one day.  During this time period the caterpillar spins a silk pad with a transverse band for the grapers in its anal prolegs to attach to, and a silk girdle across the dorsum of the 2nd-3rd abdominal segments.

Two views of a pre-pupa of the Malay Dartlet.

The pupa  secures itself to the substrate with a cremastral attachment to the silk pad and the previously constructed silk girdle. It is yellowish green throughout and has  dorsal, dorso-lateral and lateral whitish to yellowish bands. There is a long and pointed snout, and the abdomen is relatively long.  Length of pupae: 18.5-21.5mm.

A Malay Dartlet caterpillar molts to its pupal stage.

Two views of a pupa of the Malay Dartlet.

On the last day of the pupal period, the pupa becomes mostly dark brown. Yellowish orange  markings against a dark brown background are now visible in the wing cases. Finally after about 7-8 days of pupal phase, eclosion takes place with the adult emerging from the pupal case.

Two views of a mature pupa of the Malay Dartlet.

A Malay Dartlet emerges from its pupal stage.

A newly eclosed Malay Dartlet.

  • [C&P4] 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 by Horace Tan, Photos by Koh Cher Hern, Loke PF, Chng CK, Sunny Chir, Khew SK and Horace Tan

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