Species within the genus Eurema (Grass Yellows) range from Asia, Africa, Australia, and Oceania, to the Americas. 
The Grass Yellows are generally weak flyers, fluttering low around bushes and flowers.
At least 71 species are currently known. 
There are 9 species within the genus Eurema in Vietnam; Eurema brigitta, laeta, hecabe, blanda, andersoni, ada, simulatrix, novapallida and sari.
They are generally difficult to tell apart and what makes it even more difficult is that the sexes often differ slightly and there are different seasonal forms (wet and dry season forms).
The main differences between the species are:
a) the number of black spots on the underside of the forewing, combined with
b) the shape of the (apical) black markings on the upperside of the forewing and
c) the shape of the apical area markings on the underside of the forewing. 

Eurema hecabe is generally distinguished from other members of the genus by the very irregular inner margin of the dark apical band on the upperside of the forewing (evenly rounded in most other species). 
Eurema hecabe (sometimes also called Common Grass Yellow) looks very similar to the Eurema blanda (sometimes also called Three-spot Grass Yellow).
The difference, however, is on the underside of the forewing.
In Eurema blanda there are three small spots and a fourth bigger one in the middle of the wing; in Eurema hecabe there are two small spots and one bigger spot in the middle of the wing.
Eurema hecabe probably rivals Eurema blanda for the title as the most common Grass Yellow in Vietnam. 
They both are found in urban locations as well as forested areas.

1st photo: Cuc Phuong National Park, Ninh Binh, Vietnam, 12 January 2024
Last 4 photos: My Son Sanctuary, Hoi An area, Vietnam, 30 December 2023