Life History of the Common Grass Yellow

Life History of the Common Grass Yellow (Eurema hecabe contubernalis)

Butterfly Biodata:
Genus: Eurema Hübner, 1819
Species: hecabe Linnaeus, 1758
Subspecies: contubernalis Moore, 1886
Wingspan of Adult Butterfly: 35-45mm
Caterpillar Local Host Plants: Caesalpinia pulcherrima (Fabaceae, common name: Peacock Flower ), Cratoxylum cochinchinense  (Hypericaceae, common name: Yellow Cow Wood), Cratoxylum formosum (Hypericaceae, common name: Pink Mempat), Pithecellobium duice (Fabaceae, common name: Madras Thorn), Falcataria moluccana (Fabaceae, common name: Albizia), Senna spp.

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

A Common Grass Yellow resting at a leaf perch.

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. Below vein 2 of the forewing, the black border is featured at a right angle to the dorsum or sloping towards the base. Underneath, the wings are also yellow with freckled brown spots. There are typically two cell spots on the forewing - a characteristic that is mainly used to identify the lookalike species in the genus. However, some specimens of the Common Grass Yellow could exhibit variations in which only one or no cell spots are present. Males have a brand lying along the cubital vein on the forewing underside. Females are typically paler yellow with broader black border.

Another resting Common Grass Yellow.

A Common Grass Yellow taking nectar from a flower of Leea rubra.

Field Observations of Butterfly Behaviour:

Common Grass Yellow is one of the most common butterflies in Singapore. This is likely due to its many host plants being common in the wild or widely cultivated in parks and other public areas. The adults can be seen fluttering tirelessly in parks, wastelands and even  urbanised areas. They regularly visit flowers for nectar and puddle on wet grounds for minerals.

Early Stages:

The early stages of Common Grass Yellow are polyphagous with most of its host plants belonging to the Fabaceae family. The caterpillars feed on the young and tender leaves of the host plants.

Local host plant #1: Pithecellobium duice (Madras Thorn).

Local host plant #2: Caesalpinia pulcherrima (Peacock Flower).

Local host plant #3: Cratoxylum cochinchinense (Yellow Cow Wood).


Two mating pairs of the Common Grass Yellow.

The eggs of the Common Grass Yellow are laid singly on a leaf/leaflet of the host plant. The spindle shaped egg is laid standing at one end with a length of about 1.2-1.3mm. It is whitish in color and has quite a few shallow vertical ridges and indistinct horizontal striations. The micropylar sits at the tip of the standing egg.

A female Common Grass Yellow ovipositing on a leaf of the Madras Thorn.

An egg laid on a young leaf of the Peacock Flower growing in a hill park.

An egg of the Common Grass Yellow.

The egg takes about 2.5-3 days to hatch. The newly hatched has a length of about 1.8mm and has a pale whitish head capsule. It has a cylindrical and pale whitish green body covered with dorso-lateral and lateral rows of tubercles running lengthwise. Each tubercle has a setae emerging from the middle of it.  A miniscule droplet of fluid can be found at the tip of each setae.  The droplet-bearing setae is a feature seen in all five instars of the larval phase.

The dorsal view of a newly hatched caterpillar of the Common Grass Yellow, length: 1.9mm.

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 growth in this first instar is moderately paced and the body length reaches about 3.5mm in about 2-3 days before the moult to the 2nd instar.

Two view of a 1st instar caterpillar, length 3mm.

Top: A late 1st Instar caterpillar,dormant before its moult. Bottom: a newly moulted 2nd instar caterpillar, length: 3.5mm.

The 2nd instar caterpillar is yellowish green in body colour. The head capsule is similarly coloured and 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 white to yellowish band runs laterally along each side of the body. This instar is fast paced and lasts about 1-1.5 days with the body length reaching 6-6.5mm.

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

The body and the head capsule of the 3rd instar caterpillar are yellowish green. Its numerous setae are again proportionately shorter compared to the previous instar. The lateral white/yellowish bands, first appeared in the 2nd instar, has become broader and more distinct. This instar takes about 1-2.5 days to complete with body length reaching about 9mm.

Two views of a 3rd instar caterpillar, length: 7mm.

Two views of 3rd instar caterpillar, dormant prior to its moult, length: 8mm.

The appearance of the 4th instar caterpillar is little changed from the 3rd instar. The colour of both the body and the head capsule takes on a stronger green tone. This instar lasts about 1.5 days with body length reaching about 14-15mm.

Two views of a 4th instar caterpillar feeding on a leaflet, lengths: 10mm(top), 9mm(bottom).

Two views of a 4th instar caterpillar, dormant prior to its moult, length: 13mm.

The 5th and final instar caterpillar resembles the 4th instar caterpillar closely. The 5th instar lasts for 3-3.5 days, and the body length reaches up to 27mm.

Two views of a 5th instar caterpillar, newly moulted, length: 16mm.

Two views of a 5th instar caterpillar, length: 20mm.

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.

An animated sequence showing  how the caterpillar takes up the pre-pupatory pose.

A pre-pupatory larva of the Common 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: 18-20mm..

Two views of a pupa of the Common Grass Yellow.

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

After about 4 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 Common 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 Benjamin Yam, Bobby Mun, Simon Sng, Khew S K and Horace Tan

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