MORPHOLOGY

External characteristics

Male
Forewing length (mm): 39. Wingspan (mm): 63.
Forewings: Upperside dark with complete series of small submarginal spots and narrow internervular streaks; underside similar, a bit paler Hindwings very slightly crenulate, no tail; upperside dark brown, small submarginal spots, and a central white field crossed by blackened veins; underside similar, but brown paler and central field pale ochreous.

Female
Forewing length (mm): 48. Wingspan (mm):78.
As male, but internervular white much more strongly developed, so that the white color seems to be the ground color and not the brown color; also the central white field on the hindwing is much larger and reaches towards the hind margin over half of its length.

Subspecies and variation

There is quite some variation in the relative development of the dark and light parts and several individual forms have been named; part of this variation is geographical and two subspecies have been recognized.

Similar species

There is some superficial similarity with Ideopsis juventa and Tirumala hamata (both Nymphalidae: Danainae), that both are poisonous, and since it has the same flight pattern it may be mistaken for these species in the field, but a closer look shows the differences in wing pattern, and G. thule has a single anal vein in the hindwing, while the other species have two anal veins.

_{source: Jan Moonen, peronal communication 2020}