Theretra nessus (Drury, 1773)
Yam Hawk Moth
(one synonym : Sphinx equestris Fabricius, 1793)
Don Herbison-Evans,
Stella Crossley

Theretra nessus
final instar
(Picture: by Mell, 1922, courtesy of Tony Pittaway and Ian Kitching,
The Natural History Museum, London)

The Caterpillars of this species are initially green, with a yellow head, and a straightish grey spike on the tail.

The middle instars have a brown stripe along the back, a white lateral stripe along each side of the back running from the head to the base of the tail spike. They also develop some dark diagonal lines on each side of each segment, a reddish base to the tail spike, a white eyespot containing a bluish top on the first abdominal segment, and a small eyespot on each other segment, so interrupting the lateral lines.

The final instar can be similar to a middle instar, but either green or brown, with a short strong backward curving reddish tail spike.

The caterpillars are an agricultural pest, particularly feeding on :

  • Elephants Ear ( Alocasia macrorrhizos, ARACEAE ), and
  • Yam ( Dioscorea bulbifera, DIOSCOREACEAE ).

    Many other foodplants have been reported.

    The caterpillars can grow up to a length of 11 cms. The pupa is dark brown with a broad irregular pale stripes along the back, along the underside, and along each side, and large black spot on the abdominal spiracles. The pupa has a length of about 7 cms.

    Theretra nessus
    Photo: courtesy of Buck Richardson, from
    Tropical Queensland Wildlife from Dusk to Dawn Science and Art

    The adult moths have greenish-brown forewings, each with a broad pale stripe from base to wingtip, containing two closely spaced thin dark parallel lines. The hindwings are dark brown shading to a pale area at the tornus. The abdomen has a gold stripe along each side and underneath. The green colour on the wings fades to brown in dead specimens. The moth has a wingspan of about 9 cms.

    Theretra nessus
    (Specimen: courtesy of the The Australian Museum)

    The undersides are orange with some greenish-brown wiggly lines.

    Theretra nessus
    (Photo: courtesy of Ian McMillan, Imbil, Queensland)

    The coremata of the males have is composed of grey-brown hairs.

    The eggs are spherical and pale green, with a diameter up to 2mm. The eggs are laid singly on the undersides of leaves of a foodplant.

    Theretra nessus
    close-up of coremata of male
    (Photo: courtesy of Dianne Clarke, Mapleton, Queensland)

    The species is found from India to the south-west Pacific, including

  • Borneo,
  • China,
  • Hawaii,
  • Japan,
  • Philippines,
  • Thailand,

    as well as in Australia in

  • Queensland, and
  • New South Wales.

    Theretra nessus
    "Nessus Nestling Nicely"
    (Photo: courtesy of Buck Richardson, from
    Tropical Queensland Wildlife from Dusk to Dawn Science and Art)

    Further reading :

    Ian F.B. Common,
    Moths of Australia,
    Melbourne University Press, 1990, fig. 42.3, p. 415.

    Dru Drury,
    in John Obadiah Westwood:
    Figures and Descriptions of Foreign Insects,
    Illustrations of Exotic Entomology,
    Volume 2 (1773), p. 50, and also Plate 27, fig.1.

    Maxwell S. Moulds, James P. Tuttle and David A. Lane.
    Hawkmoths of Australia,
    Monographs on Australian Lepidoptera Series, Volume 13 (2020),
    pp. 254-257, Plates 66, 81, 91.

    Buck Richardson,
    Tropical Queensland Wildlife from Dusk to Dawn Science and Art,
    LeapFrogOz, Kuranda, 2015, pp. 195, 204.

    Australian Butterflies
    Australian Moths

    (updated 19 November 2011, 24 March 2017, 30 April 2020)