Circopetes obtusata (Walker, 1860)
Grey Twisted Moth
(one synonym : Arhodia modesta Warren, 1904)
OENOCHROMINAE ,   GEOMETRIDAE ,   GEOMETROIDEA
  
Don Herbison-Evans
(donherbisonevans@outlook.com)
and
Stella Crossley

Circopetes obtusata
early instars, magnified
(Photo: courtesy of Ted Cadwallader, Swan Hill, Victoria)

The colour of this caterpillar is basically brown and green. For food, our caterpillars accepted the leaves of:

  • Gum Trees ( Eucalyptus species, MYRTACEAE ),

    initially eating just a surface layer off a leaf, and cleverly attaching their scats to the edge of the leaf. More mature caterpillars ate the whole leaf.

    Circopetes obtusata
    mature caterpillar
    (Photo: courtesy of Ted Cadwallader, Swan Hill, Victoria)

    The caterpillar eventually can grow very large for a Geometrid, reaching a length of 7.5 cms. The mature caterpillar has three pairs of dorsal horns: the largest is on the first abdominal segment; a slightly smaller pair is found on the fifth abdominal segment, and the smallest pair is on the eighth abdominal segment. It can look like a stick with buds on.

    Circopetes obtusata
    mature caterpillar
    (Photo: courtesy of Merlin Crossley, Melbourne, Victoria

    Having only a single pair of ventral prolegs, a common posture is to grasp a twig with its prolegs and claspers, and a leaf with its mouth and claws. The result is a triangle, with the sides made from the twig, the leaf, and the Caterpillar. The caterpillar rarely rests lying along a twig or leaf. When it does, the body curves between the legs and the prolegs so that there is a space between the body and the twig.

    Circopetes obtusata
    pupa
    (Photo: courtesy of Ted Cadwallader, Swan Hill, Victoria)

    Prior to pupation, the caterpillar contracts slightly in length, and the skin becomes dull in colour and looks rough. The caterpillar crawls into the soil where it pupates.

    Circopetes obtusata
    (Photo: courtesy of Merlin Crossley, Melbourne, Victoria

    The adult moth is grey brown on top, with variable dark markings, and with slightly scalloped wing margins.

    Circopetes obtusata
    (Photo: courtesy of Peter Marriott, Moths of Victoria: Part 4)

    The underside is similar, but each hindwing has a small brown spot, and each forewing has three brown spots: one large and two small. The moth rests with the forewings outspread and curled, and the hindwings tucked underneath them. The moth has a wingspan of about 6 cms.

    Circopetes obtusata
    (Photo: courtesy of Bruce Anstee, Swan Hill, Victoria)

    The abdomen is often held twisted to one side, even when mating. The photos here show females bending their abdomen to the left, and males to the right. We wonder if this is genetic, or just chance?

    Circopetes obtusata
    pair of adult moths mating
    (Photo: courtesy of Anthea Flemming, Ivanhoe, Victoria,)

    The curved abdomen breaks the visual bilateral symmetry charcteristic of most animals, and makes them hard to recognize as being animals. When we first encountered a female of this species at night, beneath a mercury vapour lamp, we repeatedly overlooked the moth thinking it was a dead leaf.

    Circopetes obtusata
    Female laying eggs
    (Photo: courtesy of Bruce Anstee, Swan Hill, Victoria)

    The moth laid many eggs three days later. The eggs are small green-grey oval discs which are slightly thicker at one end. They were glued by one of their flat sides to the surface of a leaf, and often evenly spaced. The eggs hatched five days after laying.

    Circopetes obtusata
    eggs
    (Photo: courtesy of Ted Cadwallader, Swan Hill, Victoria)

    The species has been found in:

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


    Further reading :

    Ian F.B. Common,
    Moths of Australia, Melbourne University Press, 1990, fig. 54.1, p. 369.

    Pat and Mike Coupar,
    Flying Colours, New South Wales University Press, Sydney 1992, p. 42.

    Peter Marriott,
    Moths of Victoria: Part 4,
    Emeralds and Allies - GEOMETROIDEA (B)
    ,
    Entomological Society of Victoria, 2012, pp. 12-13.

    Francis Walker,
    Geometrites,
    List of the Specimens of Lepidopterous Insects in the Collection of the British Museum,
    Part 21 (1860), p. 279, No. 2.


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    (updated 18 June 2013, 20 September 2017)