Life History of the Common Dartlet

Life History of the Common Dartlet (Oriens gola pseudolus)

Butterfly Biodata:
Genus: Oriens Evans, 1932
Species: gola Moore, 1877
Sub-species: pseudolus Mabille, 1883
Wingspan of Adult Butterfly: 22-27mm
Caterpillar Local Host Plants: Ottochloa nodosa (Poaceae), Axonopus compressus (Poaceae, common names: Wide-leaved Carpet Grass, Cow Grass), Centotheca lappacea (Poaceae, common name: Sefa).

Physical Description of Adult Butterfly:

On the upperside, both sexes are dark brown with yellowish orange post-discal bands on both fore- and hindwings. The forewing band stretches from the dorsum to almost touching the costa, and is deeply excavate at vein 5. On the underside, the wings are yellowish-orange with post-discal bands mirroring those on the upperside. These bands are roughly defined by varying degrees of black shading.

Field Observations of Butterfly Behaviour:

This small and fast flying skipper is common in Singapore and can be found in parks, gardens and the nature reserve. At these locations, the adults can be seen enjoying the sun in sunny condition, typically in grassy areas or low shrubs. They visit flowers for nectar and puddle on wet ground or even bird droppings for mineral intake.

Early Stages:

The two recorded local host plants, Ottochloa nodosa and Axonopus compressus, are very common grass species in Singapore. The caterpillars of the Common Dartlet feed on leaves of the host plant, and live in shelters made by joining edges of a grass blade together with silk threads. As with other skipper species, the caterpillars have the habit of forcefully ejection their frass pellets.

Host plant #1: Ottochloa nodosa.

Host plant #2:Axonopus compressus.

A mother Common Dartlet laying an egg on a leaf of Ottochloa nodosa.

The eggs are laid singly on the underside of a leaf of the host plant. Each milk white egg is roughly hemispherical with a flattened top and its surface is finely recticulated. The base diameter is about 0.9mm.

Two views of an egg of the Common Dartlet.

Two views of a mature egg with the caterpillar in the midst of nibblying away the egg shell to emerge.

It takes about 4.5 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 1.8-1.9mm. Its creamy white body is covered with short dorso-lateral and sub-spiracular setae. A tuff of long setae can be found at the posterior end. The head capsule is entirely black and there is a black collar just behind the head on the dorsum of the prothorax.

A newly hatched 1st instar caterpillar, length: 1.9mm.

A 1st instar caterpillar in its first leaf shelter constructed at the tip of a leaf of Ottochloa nodosa. .

The leaf shelter for a first instar caterpillar on a leaf of Axonopus compressus.

The newly hatched constructs its leaf shelter soon after it is done with the egg shell. The body color changes to pale yellowish green after a few feeding sessions on the leaf. The 1st instar takes about 3-3.5 days to complete with body length reaching 4.5mm.

A late 1st instar caterpillar, dormant prior to its moult, length: 4.5mm.

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

The 2nd instar caterpillar is whitish to yellowish but with a green undertone. The anal plate still carries setae which are relatively longer. The black prothoracic collar is still present in this instar. This instar lasts about 3.5-4 days with the body length reaching about 6.5mm.

Two views of a 2nd instar caterpillar, early in this stage, length: 3.5mm.

Two views of a 2nd instar caterpillar, length: 5.5mm.

Two views of a late 2nd instar caterpillar, dormant prior to its moult, length: 6.2mm.

The 3nd instar caterpillar resembles the 2nd instar caterpillar closely in body markings and coloration except for the diminishing black prothoracic collar. Whitish dorso-lateral and lateral bands, first appears in the 2nd instar but obscure then, are now discernible. This instar lasts about 5 days with the body length reaching about 8.5-9mm.

Two views of 3rd instar caterpillar, early in this instar, length: 6.5mm.

Two views of a 3rd instar caterpillar, length: 8.5mm.

A late 3nd instar caterpillar, dormant prior to its mouilt.

The 4th instar caterpillar resembles the 3rd instar caterpillar closely but with the black prothoracic collar completely absent. The the head capsule is now pale yellowish gray with its periphery marked in black. The front cleavage lines are marked in black giving the appearance of an inverted-Y. This penultimate instar lasts 6 days with the body length reaching up to 15-16mm.

Two views of a 4th instar caterpillar, early in this stage, length: 8.5mm.

Two views of a 4th instar caterpillar, length: 12mm.

Two views of a late 4th instar caterpillar, dormant prior to its moult, length: 15.5mm.

In the 5th (and final) instar, the inverted-Y marking is thinner and discontinued near the "fork". The body is strongly whitish, with the dorsal-lateral and lateral bands whiter than the ground colour. This instar takes about 7 days to complete with the body length reaching up to about 26mm.

Two views of a newly moulted 5th instar caterpillar.

Two views of a 5th instar caterpillar, length: 21.5mm.

Two views of a 5th instar caterpillar, late in this intar, length: 25mm.

Towards the end of the 5th instar, the the body of the caterpillar shortens and its base coloration changes to a translucent green. Tyipcally it picks the underside of a grass glade to construct its pupation shelter. Within the shelter, which needs not be closed tight, it spins a silk pad and a silk girdle to secure itself. It then becomes dormant for the prepupatory phase which lasts for about 1-1.5 day.

A pre-pupa of the Common 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: 18-19mm.

Two views of a pupa of the Common 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 pads. The next day, after about 8-8.5 days of the pupal phase, eclosion takes place with the adult emerging from the pupal case.

Two views of a mature pupa of the Common Dartlet.

A newly eclosed Common Dartlet.

References:

• [C&P4] The Butterflies of The Malay Peninsula, A.S. Corbet and H.M. Pendlebury, 4th Edition, Malayan Nature Society, 1992.
• Butterflies of Thailand, Pisuth Ek-Amnuay, 2nd Edition, 2012.
• A Field Guide to the Butterflies of Singapore, Khew S.K., Ink On Paper Communications, 2010.

Text by Horace Tan, Photos by Bobby Mun, Caijin Huang, Federick Ho and Horace Tan