Papilio aegeus

Papilio aegeus Donovan, 1805
Orchard or Citrus Swallowtail
(previously known as Princeps aegeus)
PAPILIONIDAE, PAPILIONOIDEA

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

Papilio aegeus
early instar, magnified
(Photo: courtesy of Ofer Levy, Moriah College, Sydney, New South Wales)

This species is presumably named after the great King Aegeus in Ancient Greek mythology.

Although this Caterpillar is a pest on suburban Lemon trees, it is one of the most interesting caterpillars in Australia, Both its structure and its behaviour have evolved to an extraordinary degree to give it protective mechanisms against predators. It also grows into one of the largest butterflies to grace suburban gardens.

medium instar
(Photo: courtesy of Evan Harris, Ipswich, Queensland)

The early instars of this caterpillar are kite shaped, and dark brown with three white patches: one on the thorax, one above the the first pairs of prolegs, and one on abdominal segments 8 & 9. It is covered with black or white spines that are quite soft. The young caterpillar often sits by day on the top of a leaf, and resembles a bird dropping. Later instars are green with white diagonal patches.

late instar
(Photo: courtesy of Evan Harris, Ipswich, Queensland)

The last instar reaches a length of 6 centimetres, and has no spines. It is coloured yellowish green with narrow stripes or patches running obliquely upward and backward from the lower edge of the thorax to segments 4 & 6. These stripes vary in colour from pale brown to white, and are edged with iridescent mauve or blue.

The caterpillars are commonly found on the introduced members of the RUTACEAE family:

Lemon ( Citrus limon ),

Mexican Orange Blossom ( Choisya ternata ),

Cumquat ( Fortunella margarita ), and

Hardy Orange ( Poncirus trifoliata ).

The caterpillars have also been reported to feed on various Australian native plants in this same family (RUTACEAE

Common Acronychia ( Acronychia oblonga ),

Willow-leaved Crowea ( Crowea saligna ),

Desert Lime ( Eremocitrus glauca ),

Bennett's Ash ( Flindersia bennettiana ),

Australian Willow ( Geijera parviflora ),

Saffronheart ( Halfordia kendack ),

Finger lime ( Microcitrus australasica ),

Mock Orange ( Murraya paniculata ),

Satin Wood ( Zanthoxylum brachyacanthum ), and

Lanoline Bush ( Zieria smithii ).

They have also been reported feeding on plants or accepting leaves from plants from other families, including:

Jackwood ( Cryptocarya glaucescens, LAURACEAE ), and

Parsley ( Petroselinum crispum, APIACEAE ).

Those feeding on the latter developed faster than those feeding on Citrus!

early instar magnified, displaying osmeterium
(Photo: courtesy of Cameron Hayward, Denham Court, New South Wales)

When disturbed, the caterpillars are inclined to rear up at the front,and briefly evert a red forked osmeterium from behind the head. Photographing the eversion of the osmeterium is a challenge as the eversion is often very brief. At the same time as projecting the red fork, the caterpillars also produce a citrus smell.

(Photo: courtesy of Nicole Salinas)

There is evidence that the production of the smell is not actually related the erection of the osmeterium, but is a separate behaviour.

(Photo: courtesy of Trevor Jinks, North Burnett, Queensland)

The caterpillar is a very noisy chewer, making enough sound sometimes to be found by sound alone.

(Photo: courtesy of David Nelson)

The pupa is quite stout, and is grey, green or brown. It is secured to a stem of the foodplant by a cremaster and girdle. The pupa looks remarkably like a leaf. Metamorphosis may take from one to six months, depending on the season.

male
(courtesy of Megan Duckworth, Bundaberg, Queensland)

The adults have a wing span around 12 cms. The male and female butterflies differ slightly.

The male has black forewings, each with a white diagonal band across each wingtip. Each hindwing is black with a large white or cream patch, and one red spot. The underside of each forewing is grey with black veins, and has the diagonal white stripe across the wing tip. The undersides of the hindwings are black with subterminal arcs of red, white, and blue crescents.

female
(Photo: courtesy of Russell Yates, Woodgate, Queensland)

The female is similar but browner, with a large white patch on the forewings showing brown veins. Her hindwings each have a row of red chevrons and another of blue chevrons.

female, underside
(Photo: courtesy of Hugo Arnet, Kiama Downs, New South Wales)

The eggs are spherical, with a diameter of about 1 mm. Initially white, they become yellow as hatching approaches. They are laid singly on top of a leaf or shoot of a foodplant.