Butterfly of the Month - December 2023

The Cycad Blue (Theclinesthes onycha onycha) is a tiny butterfly with a big effect on its favoured host plants, much to the dread of home gardeners. The voracious larvae, laid in abundance, feed on the young growth of the plant, mostly at night while hiding at the base or under the fronds during daytime. The sheer larvae numbers leave a lasting effect and can destroy the host plant, an otherwise favourite of gardeners.

The Cycad Blue starts its life cycle as a tiny egg of 0.6mm, roughly mandarin shaped and of exquisite beauty with minute diamond shaped pits. The egg is off-white in colour, sometimes with a tinge of green or blue. The compact larvae bodies may vary in colour, starting as light green instars and transforming to dark brown before pupation. The pupa itself is light brown in base colour but adorned with darker markings. The immature stages are occasionally attended by individual ants of different families.

The adult butterfly reaches a wingspan of 2.4cm (M.F.Braby) or around 3cm (A. Orr & R. Kitching). The wing appearance can vary. The underside of male and female Cycad Blues is brown to greyish-brown with darker markings bordered by white lines across forewing and hindwing. The hindwing ends in a tail, and just above that are two black spots, one of which is encircled by an orange line. There are changes according to season with the winter colours being substantially darker.

The upper wing side of the male shows a blueish to purplish-grey infusion of the brown base colour and a dark brown outer wing edge as well as a series of black spots on the hindwing near the tail end. The female’s upper wing colour is predominantly brown with a large central blue to purplish-blue expanse on both hind and forewing. The hindwing’s outer edge near the tail shows, like in the male, a series of black spots, but more clearly encircled with a white line.

Theclinesthes onycha is the only Australian butterfly whose larvae feed on cycads. Zamiaceae and Cycadaceae are the families frequented.

Images: CM - Cliff Meyer; MP - Martin Purvis, www.purvision.com - Australian Butterflies ; PC - Peter Chew, http://www.brisbaneinsects.com/; PS - Peter Samson; SA - Sylvia Alexander, Foam Bark Gully Gang