Hyalarcta nigrescens (Doubleday, 1845)
Ribbed Case Moth
(previously known as Thyridopteryx nigrescens)
Don Herbison-Evans
Stella Crossley

Hyalarcta nigrescens
These Caterpillars live and pupate in a silken case. Initially the case has sparse bits of debris attached to it.

Hyalarcta nigrescens
early instar, magnified
(Photo: courtesy of Andy Doldissen, Sydney, New South Wales)

Later it develops several longitudinal ribs, and becomes quite bare, unlike many other species in PSYCHIDAE which cover their case in pieces of vegetation.
Hyalarcta nigrescens
Hyalarcta nigrescens
(Photo: courtesy of Bruce Anstee, Riverstone, New South Wales)
The caterpillars normally only protrude the head and thorax, which have a hard orange and dark blue skin, from their case.

The abdomen is greyish and soft, so they normally keep that inside the protective case.

Hyalarcta nigrescens
caterpillar or perhaps a flightless female inside its cut open case

The caterpillars have been found feeding on:

  • Gum Trees ( Eucalyptus, MYRTACEAE ).

    The case can grow to a length of up to 4 cms.

  • Hyalarcta nigrescens
    (Photo: courtesy of Merlin Crossley, Melbourne, Victoria)

    When metamorphosis is complete, the male extrudes the pupa from the posterior end of the case in order to emerge.

    Hyalarcta nigrescens
    male adult
    (Photo: courtesy of Merlin Crossley, Melbourne, Victoria)

    The male has a hairy black or brown head and body, with a fringe of pale hairs around the head and a tuft of yellow hairs on the tip of the abdomen. The forewings are transparent and the hindwings are variously blue, black or brown. The wingspan is about 2.5 cms.

    Hyalarcta nigrescens
    male adult
    Photo: courtesy of Buck Richardson, from
    Tropical Queensland Wildlife from Dusk to Dawn Science and Art

    The female is wingless, with a tiny head and thorax. She stays within her case for fertilisation, and lays her eggs within the case.

    Hyalarcta nigrescens
    pupa or mummified female

    When the eggs hatch, the small caterpillars move to the outside of the case and onto the food plant. Though only about 3mm long, these small caterpillars each have a small conical case, which they hold perpendicular to the surface they are on.

    Hyalarcta nigrescens
    male adult
    (Photo: courtesy of Ian McMillan, Imbil, Queensland)

    The species is found in

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

    Further reading :

    Ian F.B. Common,
    Moths of Australia,
    Melbourne University Press, 1990, p. 180.

    Edward Doubleday,
    Descriptions of some new Australian lepidopterous insects,
    in E.J. Eyre (ed.) :
    Journals of Expeditions of Discovery into Central Australia and Overland from Adelaide to King George's Sound in the Years 1840-1; sent by the colonists of South Australia, with the sanction and support of the Government: including an account of the manners and customs of the Aborigines and the state of their relations with Europeans,
    London : T. & W. Boone Vol. 1 (1845), p. 437, Plate 5, fig.1.

    Peter B. McQuillan, Jan A. Forrest, David Keane, & Roger Grund,
    Caterpillars, moths, and their plants of Southern Australia,
    Butterfly Conservation South Australia Inc., Adelaide (2019), p. 41.

    Buck Richardson,
    Tropical Queensland Wildlife from Dusk to Dawn Science and Art,
    LeapFrogOz, Kuranda, 2015, p. 184.

    Paul Zborowski and Ted Edwards,
    A Guide to Australian Moths,
    CSIRO Publishing, 2007, p. 48.

    Australian Butterflies
    Australian Moths

    (updated 25 October 2010, 2 April 2023)