Austrocaligula eucalypti (Scott, 1864)
Emperor Gum Moth
 (previously known as Antheraea eucalypti)
SATURNIIDAE,   BOMBYCOIDEA
 
Don Herbison-Evans
(donherbisonevans@yahoo.com)
and
Stella Crossley

Austrocaligula eucalypti
early instars
(Photo: courtesy of Merlin Crossley, Melbourne, Victoria)

The early instars of this Caterpillar are dark brown, with two orange spots by the head and two yellow spots by the tail. In later instars these develop into tubercles, when the first three abdominal segments develop a conspicuous orange and yellow dorsal pattern.

As the caterpillar grows, it becomes bright green on top, and still black underneath, and looks quite different. Each segment develops six tubercles with spiky yellow hairs on their tips, and the tubercles themslves are various colours. Most are yellow, but some are red, and by the head, some are purple. A yellow line runs along each side of the body, and this mimics the mid-rib of a leaf.

Austrocaligula eucalypti
caterpillar upside-down, to maximise camouflage.
(Photo: courtesy of Kevin McCue, Namadgi National Park, Australian Capital Territory)

The caterpillar feeds in daylight, and is usually upside down. Its camouflage depends on light falling on it from the right direction, as it is paler on top than underneath. If turned up the right way, it is much more conspicuous.

Austrocaligula eucalypti
caterpillar right way up, showing failure of camouflage.
(Photo: courtesy of Jackie Miles, Maffra, New South Wales)

If disturbed, the caterpillar lifts the front of its body and curls the head underneath it. In the the last instar, the underside also becomes green, and all the tubercles have purple tips.

Austrocaligula eucalypti
last instar caterpillar in defensive posture.
(Photo: courtesy of David Cook, webmaster of the Canberra Ornithologists, Wamboin, New South Wales)

The caterpillar feeds on the foliage of many plants in MYRTACEAE including:

  • various species of Gum Trees ( Eucalyptus species ),
  • Water Gum ( Tristaniopsis laurina ),
  • Brush Box ( Lophostemon confertus ), and
  • Cherry Guava ( Psidium cattleyanum ),

    and has also been found on:

  • Pepper Tree ( Schinus molle, ANACARDIACEAE ),
  • Silver Birch ( Betula pendula, BETULACEAE ),
  • Liquidambar ( Liquidambar styraciflua, HAMAMELIDACEAE ),
  • Brown Laurel ( Cryptocarya triplinervis, LAURACEAE ), and
  • Little Evodia ( Evodiella muelleri = Melicope rubra, RUTACEAE ).

    Austrocaligula eucalypti
    Australia Post, 2003

    The caterpillar grows to a length up to 8 cms. It pupates in a hard cocoon attached to the trunk of its food tree. Inside the cocoon is a brown pupa. The resting period of the pupa has been found to vary between three weeks and a year.

    Austrocaligula eucalypti
    (Photo: courtesy of the Macleay Museum, University of Sydney)

    When the moth inside the pupa is fully developed, in order to emerge from its cocoon it first scratches at one end to weaken the wall. Then using a pair of sharp hooks just behind its head, it moves round and round inside until it cuts a hole in the end of the cocoon. It then forces its way through this hole, and immediately climbs to a position where it can hang upside down to expand its wings.

    Austrocaligula eucalypti
    relaxed pose
    (Photo: courtesy of Merlin Crosley)

    The moth is brown with shades varying from yellowish to reddish. The moths have wrinkled wingtips, and a small thin dark-edged white triangle near the leading edge of each forewing, about one quarter the way along. Each wing has a single eyespot in the middle. This is a dull pink on the forewings, and a more spectacular red with a black circle on the hindwings.

    Opodiphthera eucalypti
    alarmed pose
    (Photo: courtesy of Merlin Crosley)

    The moth usually rests with the forewings covering the hind eyespots, and exposes them if disturbed. The moths also tend to bend their abdomen to one side, which presumably breaks the bilateral symmetry, making it less recognisable as an animal. The wingspan is usually in the range 8 to 13 cms.

    Austrocaligula eucalypti
    with bent abdomen
    (Photo: courtesy of Barb Evans, Eurobin, Victoria)

    The adult moths have degenerate mouthparts, and so cannot feed. They rely for energy solely on the food ingested by the Caterpillars, earlier in their lives.

    Austrocaligula eucalypti
    female
    (Photo: courtesy of Steven Dodge, Nowra, New South Wales)

    The males and females differ most obviously in the antennae: the females having thread-like antennae, and the males feathery antennae.

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

    The eggs are oval and off-white, darkening as hatching approaches. They are laid in an irregular clusters of around 30 at a time.

    Austrocaligula eucalypti
    eggs
    (Photo: courtesy of Dianne Clarke, Mapleton, Queensland)

    The species occurs in

  • New Zealand

    as well as over most of Australia, including:

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

    Austrocaligula eucalypti
    female, showing underside
    (Photo: courtesy of Emma Moysey, Ecology Australia Pty. Ltd.)

    This species was moved from the genus Opodiphthera to Austrocaligula by Brechlin in 2005, and many Taxonomists disagree with this reassignment. Here, we follow Brechlin in this most recent publication on this family.

    Further reading :

    Ronald Brechlin,
    Einige Anmerkungen zur Gattung Neodiphthera Fletcher, 1982 stat. rev. mit Beschreibung von vier neuen Arten (Lepidoptera: Saturniidae),
    Nachrichten des Entomologischen Vereins Apollo,
    N.F. 26 , Parts 1/2 (2005), pp. 17–29.

    Ian F.B. Common,
    Moths of Australia,
    Melbourne University Press, 1990, pls. 15.1, 28.9, pp. 34, 57, 403, 405,
    (listed as Opodiphthera eucalypti).

    Pat and Mike Coupar,
    Flying Colours,
    New South Wales University Press, Sydney 1992, p. 85.

    David Carter,
    Butterflies and Moths,
    Collins Eyewitness Handbooks, Sydney 1992, p. 231.

    Densey Clyne,
    Emperor's New Clothes,
    Metamorphosis Australia,
    Issue 72, March 2014, pp. 1,4-7,
    Butterfly and Other Invertebrates Club Inc.

    Peter Hendry,
    Saturniidae,
    Metamorphosis Australia,
    Issue 51, December 2008, pp. 27-29,
    Butterfly and Other Invertebrates Club Inc.

    Peter Marriott,
    Moths of Victoria - Part 1,
    Silk Moths and Allies - BOMBYCOIDEA    ,
    Entomological Society of Victoria, 2008, pp. 26-27.

    Buck Richardson,
    Tropical Queensland Wildlife from Dusk to Dawn Science and Art,
    LeapFrogOz, Kuranda, 2015, p. 193.

    Harriet, Helena, and Alexander W. Scott,
    Australian Lepidoptera and their Transformations,
    Australian Lepidoptera,
    Volume 1 (1864), pp. 1-3, and also Plate 1.

    Paul Zborowski and Ted Edwards,
    A Guide to Australian Moths,
    CSIRO Publishing, 2007, pp. 20, 162.

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    (updated 16 September 2008, 17 July 2018, 15 September 2019, 4 October 2020, 21 April 2022)