Common Grass Yellow

The common grass yellow exhibits seasonal polyphenism. The lepidopteran has a darker summer morph, triggered by a long day exceeding 13 hours in duration, while the shorter diurnal period of 12 hours or less induces a fairer morph in the post-monsoon period.

Male. Upperside (dorsal surface): yellow, variable in tint from sulphur to rich lemon yellow according to season and locality. Forewing: apex and termen deep black, this colour continued narrowly along the costal margin to base of wing, near which it often becomes diffuse; the inner margin of the black area from costa to vein 4 very oblique and irregular, between veins 2 and 4 excavate on the inner side, this excavation outwardly rounded between the veins and inwardly toothed on vein 3; below vein 2 the black area is suddenly dilated into a square spot which occupies the whole of the tornal angle; the inner margin of this dilatation is variable, in the typical form slightly concave. …

Eggs are laid on Abrus precatorius, Falcataria moluccana, Acacia sp., Aeschynomene species and numerous other Leguminosae, Euphorbiaceae and Cucurbitaceae sp.. Studies suggest that the females can discriminate colours when choosing host plants for oviposition. Larva: "Long, green, rough, cylindrical, or slightly depressed, with a large head." Pupa: "Suspended by the tail and by a moderately long band; the abdominal segments are round, but the thorax is much compressed, the wing-cases uniting to form a deep sharp keel. The head-case terminates in a short pointed snout. Ordinarily the pupa is solitary and green, but sometimes on a twig in large numbers. Many Pierine and other larvae seek each others company at that time. Having selected a dead branch of some neighbouring bush, they acquired the colour of their surroundings as nearly all Pierine and Papilionine pupae do to a greater or less extent." This species has been found to be parasitised by multiple strains of Wolbachia. These bacteria can alter the sex ratios of the species.