SOUTH AUSTRALIAN SUN-MOTHS


The sun-moths belong in the Castniidae Family, which in the Australian Region presently contains the single genus Synemon Doubleday, 1846. They are dayflying moths, small to medium in size with a wing expanse of 25-55 mm. The forewings are a cryptic brown or grey colour, but their hindwings usually contain bright red, orange or yellow colours that are used as a sudden flash-display mechanism.  They are often mistaken for butterflies and skippers, and even have clubbed antennae similar to butterflies, but the hindwings have a frenulum. In some species like Synemon plana (Golden Sun-moth) the sexes are strongly dimorphic with the female having bright yellow hindwings, whereas the male has dull brown hindwings.

The moths are restricted to the temperate and tropical habitat areas of mainland Australia, and are absent from the very arid inland areas and on Tasmania. They fly rapidly in sunshine, close to the ground.  The moths rest on the ground or on grasses and low plants, with the forewings covering the hindwings.  In warm conditions resting moths are very timid and can be very difficult to approach. They inhabit grasslands and low sedge-rush lands or very open woodlands that contain their hostplants in the understorey. Their habitat has suffered drastic fragmentation and alteration due to agriculturalisation, pastoralisation and urbanisation, and many species are threatened. Flight times are mainly during spring and summer, but some species such as Synemon selene (Pale Sun-moth) fly during autumn.

Eggs are elongate ellipsoidal with prominent longitudinal and finer lateral ridges. The female is endowed with a long tubular spine-like ovipositor at the end of the abdomen, used to penetrate into the base of their hostplants to deposit the eggs in crevices near soil level.  The larvae feed on grasses, low tussock sedges and mat-rushes.  The larvae are of witchetty or bardi grub form, white when young but can be pink, red or orange near maturity.  They usually live and feed at the base of the hostplant when immature, but  tunnel deeper underground to the root zone when mature, to feed on roots.  This latter adapation would likely protect the larvae from the above-ground effects of drought, dry summer conditions and infrequent fires, but has not protected them from the modern farming practices of tillage, overgrazing and trampling by stock, use of broad-acre insecticides and herbicides, and frequent fires. Pupation either occurs within the root zone or deeper part of the hostplant, or in the soil at the end of a silk-lined tunnel peripheral to the hostplant, and the empty pupa case (exuvia) is left protruding from the tunnel at ground level after the moth emerges.  The pupa is brown with one or two transverse rows of dorsal spines on the abdomen. Some isolated small populations of S. selene form parthenogenic female groups.   Studies indicate the early-stage brood period generally requires two years to complete, but may be less for smaller species, or longer for larger species depending on the environmental or climatic conditions at the time. Mature larvae are known to become torpid and delay pupation during poor conditions.

There are about 24 recognised species in Australia, and there are possibly more than 20 unamed species.  Many of the latter comprise populations that are very similar and difficult to separate, and will likely require DNA analysis to establish their true taxonomic relationships.  Seven named species have been recorded from South Australia, and a further three species are presently unamed or require further study.

 

Synemon discalis Strand, 1911 (Small Orange-spotted Sun-moth). Wing Expanse: 30-42mm. Known Distribution: Southern Eyre Peninsula, Southern Yorke Peninsula, Upper Southeast. Flight Time: Oct-early Nov. Known Hostplants: Gahnia lanigera and other small sedges (Cyperaceae) and possibly Austrostipa sp incl A. mundula (Poaceae).

Synemon jcaria R. Felder, 1874 (Reddish-orange Sun-moth).  Wing Expanse: 34-40mm. Known Distribution: Upper Southeast. Flight Time: late Jan-mid Mar. Known Hostplants: Lomandra effusa (Asparagaceae).

Synemon nais Klug, 1850 (Orange Sun-moth). Wing Expanse: 27-30mm. Known Distribution: East Nullarbor Plains, Far West Coast, Yorke Peninsula, Pinnaroo. Flight Time: late Sep-mid Nov. Known Hostplants: Austrodanthonia setacea and Austrostipa eremophila (Poaceae).

Synemon parthenoides R. Felder, 1874 (Orange-spotted Sun-moth). Wing Expanse: 35-52mm. Known Distribution: Eyre Peninsula, Yorke Peninsula, Mt Lofty Ranges, Kangaroo Island, Upper South East. Flight Time: late October-Jan, rarely to late Feb. Known Hostplants: Lepidosperma carphoides (Cyperaceae).

Synemon plana Walker, 1854 (Golden Sun-moth). Wing Expanse: 31-35mm. Known Distribution: Bordertown in buloke grasslands. Flight Time: Aug-Mar, mainly Nov-Jan. Known Hostplants: Austrodanthonia carphoides, A. laevis, A. setacea (Poaceae).

Synemon selene Klug, 1850 (Pale Sun-moth). Wing Expanse: 35-52mm. Known Distribution: Adelaide Plains-Two Wells, Lyndoch, Renmark. Flight Time: early Feb-early Mar. Known Hostplants: Austrodanthonia setacea (Poaceae).

Synemon theresa Doubleday, 1846 (Cryptic Sun-moth). Wing Expanse: 28-40mm. Known Distribution: Mt Lofty Ranges, Parkside. Flight Time: Dec-mid Mar. Known Hostplants: Austrodanthonia caespitosa (Poaceae).

Synemon sp (Ignita Sun-moth). Wing Expanse: 40-52mm. Known Distribution: Kangaroo Island. Flight Time: Jan. Known Hostplants: Lepidosperma viscidum (Cyperaceae).

Synemon sp (Flinders Ranges Sun-moth). Known Distribution: Flinders Ranges. Flight Time: late Oct-early Nov. Known Hostplants: A (Poaceae).

Synemon sp (Colona Sun-moth).Wing Expanse: 26mm. Known Distribution: Colona. Flight Time: late Mar. Known Hostplants: Austrostipa eremophila (Poaceae).

 

 

 

First instar larva

Photography by R. Grund

 

Author:  R. GRUND, copyright 23 May 2009, all rights reserved.   Last update 23 May 2009.