Opodiphthera eucalypti

Opodiphthera eucalypti (Scott, 1864)
(previously known as Antheraea eucalypti)
Emperor Gum Moth
SATURNIIDAE

Don Herbison-Evans ( donherbisonevans@yahoo.com )
&
Stella Crossley

(updated 25 January 2008)

early instars
(Photo: courtesy of Merlin Crossley)

This Caterpillar starts off life as one of a row or cluster of a dozen yellowish eggs laid on a leaf of a food plant. The early instars are dark brown, with two orange spots by the head and two yellow spots by the tail. These develop in later instars into tubercles, when the first three abdominal segments develop a conspicuous orange and yellow dorsal pattern.

later instar
Caterpillar is upside-down, to maximise camouflage.
(Photo: courtesy of Jan MacDonald, Finch Hatton, near Mackay, Queensland)

As the Caterpillar grows, it becomes bright green 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.

Caterpillar in defensive posture.
(Photo: courtesy of David Cook, webmaster of the Canberra Ornithologists, Wamboin, NSW)

If disturbed, the caterpillar lifts the front of its body and curls the head underneath it. It 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.

Caterpillar right way up, showing failure of camouflage.
(Photo: courtesy of Merlin Crossley)

It feeds on:

various species of Gum Trees ( Eucalyptus, MYRTACEAE ),

Water Gum ( Tristaniopsis laurina, MYRTACEAE ),

Brush Box ( Lophostemon confertus, MYRTACEAE ),

and has also been found on:

Pepper Tree ( Schinus molle, ANACARDIACEAE ),

Silver Birch ( Betula pendula, BETULACEAE ),

Liquidambar ( Liquidambar styraciflua, HAMAMELIDACEAE ), and

Brown Laurel ( Cryptocarya triplinervis, LAURACEAE ).

It grows to a length of about 6 cms. The Caterpillar 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.

(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.

female
(Photo: courtesy of Emma Moysey, Ecology Australia Pty. Ltd.)

The moth is a variable shade of brown, with wrinkled wingtips, and with a small thin 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 spectacular red with a black circle on the hind wings.

(Photo: courtesy of Barb Evans, Eurobin)

The moth usually rests with the forewings covering the hind eyespots, and exposes them if disturbed. The wingspan is usually in the range 8 to 13 cms.

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.

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

The species occurs over most of Australia.

( Australia Post, 2003)