Thalaina selenaea (Doubleday, 1845)
Orange-rimmed Satin Moth
(one synonym : Absyrtes fortunata Thierry-Mieg, 1899)
NACOPHORINI ,   ENNOMINAE ,   GEOMETRIDAE ,   GEOMETROIDEA
 
Don Herbison-Evans
(donherbisonevans@outlook.com)
and
Cathy Young & Stella Crossley


early instar, magnified
(Photo: courtesy of Cathy Young)

Initially these Caterpillars are a green with long sparse black hairs and a red area behind the head.


(Photo: courtesy of Merlin Crossley, Melbourne, Victoria)

Later as they grow, they become smooth and green with a number of dorsal white lines along the body, and a lateral yellow line along each side. These serve to hide the Caterpillars well amongst the leaflets of their foodplant. They also have a pair of projections on the head tipped with red, which although harmless, may serve to ward off predators.

There are three pairs of ventral prolegs, of which the first two pairs are reduced. During movement along a twig, the middle pair touches the twig but does not clasp it. Only the last pair appear to function as legs.


(Photo: courtesy of Wendy Moore, Melbourne, Victoria)

In colour and markings, this caterpillar is very similar to that of Thalaina clara, but our specimens could be distinguished because they lacked the wavy outline and ringed markings present in Thalaina clara. The timing of the life cycle stages is similar in both species, the Caterpillars being found in Melbourne from June to August. The behaviour of the Caterpillars of the two species is also similar.

The Caterpillars have been found feeding on various Wattles ( MIMOSACEAE ) including:

  • Silver Wattle ( Acacia dealbata ), and
  • Blackwood ( Acacia melanoxylon ).

    The caterpillars have been observed specifically to eat the stalk of the pinnules of the bipinnate wattle form, and as a Caterpillar fed, the pinnules became detached, and adhered to its head or fell to the floor. The caterpillar seemed happy to eat the phyllodes of the broad-leafed wattle. The caterpillars characteristically stand on their tail, resembling a Praying Mantis. Their head was observed to turn toward a bright light.

    The caterpillars grow to a length of about 4 cms. They pupate in loose cocoon in the soil or leaf debris. The pupal duration is about eight months.

    The adult is silky white, with a rusty mark along the costas of the forewings near the head, and along the margins.


    Pure white form
    (Photo: courtesy of Cathy Young)

    Some specimens have a rust coloured stripe diagonally across each forewing.


    (Specimen: courtesy of the Macleay Museum, University of Sydney)

    There is an orange and brown spot on the undersurface of each hindwing which may be visible on the upper surface. The moth has a wingspan of about 5 cms.


    underside
    (Photo: courtesy of Wendy Moore, Melbourne, Victoria)

    The females scatter their eggs. The eggs are bullet-shaped, with a flat end that is covered in microscopic dimples, Initially the eggs are light green, but they darken through purple as hatching approaches.


    eggs magnified
    (Photo: courtesy of Cathy Young)

    The species occurs in

  • New South Wales,
  • Australian Capital Territory,
  • Victoria,
  • Tasmania, and
  • South Australia.

    In Melbourne, the adults are most common in Autumn, particularly in April.


    Further reading :

    Pat and Mike Coupar,
    Flying Colours,
    New South Wales University Press, Sydney 1992, p. 53.

    Edward Doubleday,
    Descriptions of some new Australian lepidopterous insects,
    in E.J. Eyre, E.J. (ed.) : Journals of Expeditions of Discovery into Central Australia,
    London : T. & W. Boone (1845) , Vol. 1, p. 437, Plate VI, fig. 2.

    Marilyn Hewish,
    Moths of Victoria: Part 5,
    Satin Moths and Allies - GEOMETROIDEA (A)
    ,
    Entomological Society of Victoria, 2014, pp. 2, 18-19, 30-31.

    Peter B. McQuillan,
    A review of the Australian moth genus Thalaina (Lepidoptera: Geometridae: Ennominae),
    Transactions of the Royal Society of South Australia.
    Volume 105, Issue 1 (1981) pp. 1-23.

    Peter B. McQuillan,
    An overview of the Tasmanian geometrid moth fauna (Lepidoptera: Geometridae) and its conservation status,
    Journal of Insect Conservation,
    Volume 8 (2004), Parts 2-3, pp. 209-220.

    Cathy Young,
    Characterisation of the Australian Nacophorini and a Phylogeny for the Geometridae from Molecular and Morphological Data,
    Ph.D. thesis, University of Tasmania, 2003.


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    (updated 17 September 2011, 7 June 2014)