Butterfly of the Month - February 2024

The Large Grass Yellow (Eurema hecabe) is a much loved butterfly, quite common not least because of the variety of host plants the larvae use as food source.

With a wingspan of 37mm for the male and 40mm for the female it’s one of the smaller butterflies (although size may vary), but very noticeable with its predominantly yellow wing colours. As there are similar looking butterflies, the key features for identification are found in the size of the species and in the markings on the upper side of the wings.

While Eurema hecabe’s base colour is yellow like on the underside, the forewing has black edge markings with distinct indentations. They are wide in the forewing and much narrower in the hind wing. We recommend you use a field guide like Michael F. Braby’s The Complete Field Guide to Butterflies of Australia to help the identification process. The species which is closest in appearance (E. alitha) is substantially smaller.

The butterfly’s underside is again yellow without the distinct black edges of the upper side, but brown markings across fore and hindwings. The patterns may vary especially in colour intensity between wet and dry season or show themselves in a transitional form. While the wet season markings are somewhat faint, the dry season markings are pronounced.

The Common Grass Yellow starts its life cycle as a tiny egg, 1.3mm high and only 0.5mm wide. It has the shape of a spindle, and under magnification light vertical striations can be seen. The female lays her eggs singly onto leaves. While our image shows a preference for younger leaves, older leaves are used as well.

Once hatched, the green larva can reach 30mm in its late instar stage. It is adorned with a white horizontal line and multiple short hairs.

The pupa is affixed to a stem of the host plant. It is suspended and held by cremaster (stem like appendage) and girdle like most other species, but E. hecabe’s pupa is situated almost horizontally, often resembling a leaf. In our image the butterfly is near eclosing (emerging from the pupa as an adult). You can already see the upper wing markings shining through.

Larval host plants for the Large Grass Yellow are numerous. Among them are Coffee Bush (Breynia oblongifolia), misc. wattles including Acacia maidenaii and A. melanoxylon, Yellow Pea-bush (Sesbania cannabia), misc. Senna species including S. acclinis and S. gaudichaudii, Butterbush (Chamaecrista nomame) and others.

Images: CM - Cliff Meyer; DM - Deborah Metters; PH - Peter Hendry; RM - Robert (Bob) Miller; SEC - School of Ecology and Conservation, UAS Bangalore, CC BY SA 2.5