Life History of the Chocolate Grass Yellow

Life History of the Chocolate Grass Yellow (Eurema sari sodalis)

Butterfly Biodata:
Genus: Eurema Hübner, 1819
Species: sari Horsfield, 1829
Subspecies: sodalis Moore, 1886
Wingspan of Adult Butterfly: 35-40mm
Caterpillar Local Host Plant: Archidendron jiringa (Fabaceae, common name: Greater Grasshopper Tree, Petai Belalang).

A Chocolate Grass Yellow puddling on wet ground for minerals.

Another puddling Chocolate Grass Yellow.

Physical Description of Adult Butterfly:

Above, the wings are deep lemon-yellow, each with a black border which is regularly scalloped and deeply excavated between veins 2 and 4 in the forewing. Underneath, the wings are yellow with freckled brown spots. There is one cell spot on the forewing which has its apex entirely in dark brown. Males have a brand lying along the cubital vein on the forewing underside.

A Chocolate Grass Yellow taking nectar from Syzygium flowers.

A Chocolate Grass Yellow visiting a tiny flower for nectar.

Field Observations of Butterfly Behaviour:

Chocolate Grass Yellow is common in both nature reserves and urban parks in Singapore. The adults can be readily seen fluttering tirelessly in these areas. They are easily confused with other Grass Yellow spp. while in flight, but their distinctive brown forewing apical area immediately set them apart when they come to a perch. They regularly visit flowers for nectar and puddle on wet grounds for minerals.

A Chocolate Grass Yellow taking nectar from a flower of Leea indica.

A group of puddling Chocolate Grass Yellow sighted on a foot path in the nature reserve.

Early Stages:

Only one local host plant, Archidendron jiringa, has been recorded for Chocolate Grass Yellow. This plant is common throughout the nature reserves, areas in Singapore Botanical Gardens and Southern Ranges. The caterpillars feed on the young and tender leaves of the host plant.

Local host plant: Archidendron jiringa.

A mating pair of the Chocolate Grass Yellow.

The eggs of the Chocolate Grass Yellow are laid singly on a leaflet of the host plant. At times, a number of eggs could be found on a single leaflet from repeated oviposition visits by several females. The spindle shaped egg is laid standing at one end with a length of about 1.4mm. It is whitish in color and has indistinct shallow vertical ridges. The micropylar sits at the tip of the standing egg.

A few eggs of Chocolate Grass Yellow laid on young leaves of the local host plant.

An egg of the Chocolate Grass Yellow.

The egg takes about 2.5-3 days to hatch. The newly hatched has a length of about 2.4mm and has a pale whitish head capsule. It has a cylindrical and pale whitish body covered with dorso-lateral and lateral rows of tubercles running lengthwise. As is the case for other Eurema spp., each tubercle has a seta emerging from the middle of it with the tip of the seta bearing a droplet-like structure. These droplet-bearing setae is a feature seen in all five instars of the larval phase.

Two views of a newly hatched caterpillar of the Chocolate Grass Yellow.

After hatching, the young caterpillar eats the empty egg shell for its first meal, and then moves on to eat the leaf lamina for subsequent meals. The body colour turns yellowish green as growth progresses. The body length reaches 4.8mm in about 2 days before the moult to the 2nd instar.

Two view of a 1st instar caterpillar, length 3.9mm.

The 2nd instar caterpillar is yellowish green in body colour. The yellow head capsule has the same tiny setae-bearing tubercles as those on the body surface. Compared to those in the previous instar, these setae carpeting the body and head capsule are proportionately shorter and greater in number. A pale yellowish band runs laterally along each side of the body. This instar is fast paced and lasts about 1 day with the body length reaching 7mm.

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

The 3rd instar caterpillar resembles the 2nd instar caterpillar closely with a yellow head and a yellowish green body. Its numerous setae are again proportionately shorter compared to the previous instar. Equally fast paced, this instar takes about 1-1.5 days to complete with body length reaching about 10-11mm.

Two views of a newly moulted 3rd instar caterpillar.

Two views of 3rd instar caterpillar, length: 9mm.

Caterpillars of the Chocolate Grass Yellow sighted in the field. Two to each of the two panels, can you spot them?

The body and the head capsule of the 4th instar caterpillar are pale greenish to yellowish green. The lateral yellowish bands, first appeared in the 2nd instar, have become whitish and more distinct. This instar takes about 1-1.5 days to complete with body length reaching about 17mm.

Two views of a 4th instar caterpillar, length: 17mm.

The 5th and final instar caterpillar resembles the 4th instar caterpillar closely. The whitish lateral bands are broader and more distinct. The numerous setae-bearing tubercles are more prominent as they appear in darker green in contrast to the paler body base colour. The 5th (and final) instar lasts for 3.5-4 days, and the body length reaches up to 30mm.

Two views of a 5th instar caterpillar, early in this stage, length: 17mm.

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

On the last day of the 5th instar, the body of the caterpillar shortens and changes to either a dull shade or bright shade of green. It ceases feeding and comes to a halt on the underside of a stem/stalk on the host plant. Here the caterpillar spins a silk pad and a silk girdle. With its posterior end secured to the silk pad via claspers, and the body suspended at the mid-section with the girdle, the caterpillar soon becomes immobile in this pre-pupatory pose.

A pre-pupatory larva of the Chocolate Grass Yellow.

Pupation takes place about 0.5 day later. The yellowish green pupa secures itself with the same silk girdle as in the pre-pupal stage, but with the cremaster replacing claspers in attaching the posterior end to the silk pad, The pupa has a pointed head and a keeled wing pad, and its  body is  mostly unmarked except for a faint pale brownish and narrow dorsal band. Length of pupae: 19-20mm..

The pupation event of two Chocolate Grass Yellow caterpillars in close proximity.

Two views of a pupa of the Chocolate Grass Yellow.

Two views of a mature pupa of the Chocolate Grass Yellow.
The now transparent wing pad shows the yellow forewing upperside with its black border.

After about 5 days of development, the pupal skin turns translucent as the development within the pupal case comes to an end. The yellow coloration and back borders on the forewing upperside are now discernible. The following day, the adult butterfly emerges from the pupal case.

A newly eclosed Chocolate Grass Yellow clinging onto its empty pupal case.

References:

• [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, 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 PF Loke, Antonio Giudici, Federick Ho, Khew S K and Horace Tan

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