Common Grass Yellow Caterpillar

I found this caterpillar of Common Grass Yellow on Peacock Flower in my garden. This looked like the 5th Instar of the caterpillar stage. I was using a Canon EOS 5DS R with Canon EF 100mm f/2.8L Macro IS USM lens, illuminated by Godox Ving V860c E-TTL Li-ion Flash with LumiQuest SoftBox III to capture this caterpillar.

The Common Grass Yellow or Large Grass Yellow (Eurema hecabe) is a small butterfly (wingspan 35-40 mm) in family Pieridae. Adult butterfly upperside of the wings is bright yellow with the fore wing having broadly black excavated border in the apex and termen and hind wing with narrow irregular border. Underside of both wings is yellow with dark brown markings and irregular shaped rings. The female is large and paler than male.

Host plants for the caterpillar are 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.

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. 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.

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.

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.

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.

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.

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.

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.

Pupation takes place about half a 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.

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.