The Common Grass Yellow butterfly, also known as Eurema Hecabe, is a small, charming butterfly species that can be found across Asia, North America, Africa, and Australia. These butterflies love zipping around close to the ground, and you can often find them in open, grassy, or bushy areas – that's how they got their name! These little beauties have vibrant yellow wings that can range from a sultry sulfur shade to a lush lemon yellow, shifting with the seasons and their location. You'll typically see male Common Grass Yellow butterflies hanging out in large groups, while the females fly solo, seeking out nectar from a diverse array of plants.
These butterflies have two unique forms: the "wet-season form" and the "dry-season form." During warmer or wetter months, you'll find the wet-season Common Grass Yellow butterflies displaying a darker yellow tone on their wings. This helps them blend into the dry, brown vegetation around them. On the other hand, when cooler or drier months arrive, the dry-season form makes an appearance with its light yellow coloration that helps it camouflage among lush green plants.
Male Common Grass Yellow butterflies have bright yellow wings with black borders on top, while underneath they show off pale yellow wings with black spots. Females have similar patterns, but their black borders are slightly wider. Both males and females have reddish-brown markings on their forewings and rows of small marks on their hind wings when viewed from below. One distinguishing feature is that male butterflies have a thick vein called the sex mark on their forewing – which isn't present in females.
The life of a Common Grass Yellow butterfly goes through four stages: egg, caterpillar (larva), pupa, and finally adult butterfly. First up is egg-laying; the mother butterfly carefully deposits her spindle-shaped white eggs one at a time on the host plant's leaves. After about three days, these eggs hatch to reveal tiny caterpillars that first feast on their hatched eggshells before munching away at their leafy surroundings. As they grow, their bodies turn into an appetizing shade of yellowish-green.
When it's time for the caterpillar to transform into a pupa, it shortens its body and turns into a green shade. It then stops eating, finds a cozy spot under a stem or stalk of its preferred plant, and spins a silk pad and girdle for support. Pupation begins within just one day. The resulting yellowish-green pupa measures about 18-20mm long, with a pointed head, a keeled wing pad, and minimal other markings apart from a soft brownish dorsal stripe.
After around four days inside the pupa, you can start noticing changes – the pupal skin becomes more transparent, revealing the yellow color and dark wing edges of the developing adult butterfly inside. The very next day, the fully formed butterfly finally emerges with a wingspan of 35-45mm.
You can find plenty of Common Grass Yellow butterflies in Nepal, where they thrive all year round with abundance during the sunny summer months.