GOLDEN SUN MOTH – Synemon plana
Story by Clive Crouch (OAM) – Clive Crouch Environmental Research (All information and text is subject to copyright and cannot be reproduced without permission)
STATUS – CRITICALLY ENDANGERED
LOCATION – Native Grasslands of Australia
A BRIEF HISTORY OF THE NHILL SUN-MOTH RESERVE
Fifty million years ago, as the super-continent of Gondwana was in its final stages of breaking up and drifting apart, grasses and other flowering plants were beginning to appear, along with the ancestors of today’s moths and butterflies.
From these ancestral Gondwana stocks, a rich and diverse moth and butterfly fauna developed on the Australian continent, including the Australian representatives of the modern-day Sun-moths, which are unusual in that they are neither a typical moth or a butterfly; they have clubbed antennae and are day-flying like butterflies.
Several species of Sun-moths were common and widespread across southern Australia when Europeans first arrived, but as land was cleared for agriculture our native grasslands, on which many species of Sun-moths depend, began to decline to the point where less than 0.5% remains today. As our native grasslands disappeared, so did the native species of flora and fauna that depend on it for their survival. Today, all but one of Victoria’s eight species of Sun-moth is endangered. The township of Nhill in Victoria’s west revealed to be home to the largest Golden Sun-moth populations by local entomologist Fabian Douglas and due to the unusually large and dense population within an undeveloped housing estate, moves were made to protect this site from the proposed development.
As part of his research, Fabian visited the insect collection at the National Museum of Victoria in Melbourne. Amongst the collection of Sun-moths was a single specimen of the Pale Sun-moth – Synemon selene, collected by a Rev.A.J. Fidian in Nhill in 1902 that was unlike any other Pale Sun-moth he had seen. Fabian began to think that, as this housing estate had such a large population of the Golden Sun-moth, might it be possible that the Pale Sun-moth could still occur there too?
In February 1998, to his great delight, Fabian found that the Nhill form of the Pale Sun-moth still existed there in good numbers, despite the fact that it was known only from a single specimen collected 96 years earlier. Due to this discovery, it now appeared that this housing estate was the only place in the world that now held and extant (still existing, not extinct) population of this unique form of the Pale Sun-moth. This made the preservation of the housing estate even more imperative and with the wonderful support from the Hindmarsh Shire, Trust for Nature, the World Wildlife Fund and the R.E. Ross Trust; the area has now been formally set aside as the ‘Nhill Sun-moth Reserve’…. but then Fabian made and even more startling discovery! All of the Victorian populations of Pale Sun-moths are parthenogenic – that is, there are no males in these populations. Females lay fertile eggs without the need for the eggs to be fertilised by a male! Normally, in parthenogenic species, all offspring are a clone of the mother and they are all identical, but amazingly in Victoria, there are five different morphs (forms) of the Pale Sun-moth. If Fabian can work out the mechanics of how this happened, the implications for the billion-dollar animal husbandry industry will be enourmous.
To lose species like Nhill’s fabulous Sun-moths before scientists have fully investigated them would be akin to the Galapagos Islands disappearing before Charles Darwin conducted his famous studies there on the origin of species.
DESCRIBING THE GOLDEN SUN MOTH
Two critically endangered Sun-moths are found on the Nhill Sun-Moth Reserve; the Golden Sun-moth – Synemon plana and the Nhill morph of the Pale Sun-moth – Synemon slene. Both species appear to be dependent on the Bristly Wallaby Grass – Austrodanthonia setacea for their larval food supply.
The Golden Sun-moth emerges in late October to mid November and has a flight period extending over approximately a three week period, but individuals of both species survive for only a few days. When they emerge as adults, they have no functional mouth parts and so are unable to feed, therefore they have to rely on a limited reserve of fat stored in their bodies to sustain them until they have completed their life cycles; laying eggs that will in time become the next generation of Sun-moths.
The Synemon plana species has both males and females in it’s populations, as is the case with most species. When they emerge as adults, the females are full of eggs and are almost flightless, fluttering only a meter or so, if hard pressed. The males on the other hand, are very active fliers. The females usually sit at the base of a clump of Wallaby Grass and when they see a male fly pass, they open their fore-wings to expose their bright golden-yellow hind-wings. The males fly rapidly, about a metre above the ground, patrolling a large area and when they see the flash of colour from the females display, they land and mate with her. After being fertilized, the female then walks from one tussock of Wallaby Grass to the next depositing her eggs at the base of the clumps. When the eggs hatch, the little caterpillars burrow down into the soil and feed on the roots of the Wallaby Grass, eventually metamorphosing into a chrysalis and in time, will emerge as a flying adult Sun-moth.
The Pale Sun-moth – Synemon selene is the most unusual, in that within Victoria it is parthenogenic – that is, there are no males in the Victorian populations. Females lay fertile eggs that produce only female off-spring. In all other respects, the life-cycle of this species is very similar to that of the Golden Sun-moth, except the females are very strong fliers.
The continued survival of these critically endangered Sun-moths at Nhill is dependent upon correct management of this reserve. This includes ensuring the preservation of the Wallaby Grass on which the Sun-moths rely on for food; suppression of weeds, mowing and/or grazing by sheep at times to ensure that it is kept at the optimum height and condition, as well as the ongoing monitoring of Sun-moth populations. The principal reason for the current precarious position of the Sun-moths and many other grassland species of flora and fauna, is the loss of native grassland due mainly to cultivation and the use of fertilisers for agriculture purposes. The Sun-moths have survived in the Nhill reserve only because it has never been cultivated and the use of fertilisers applied to the habitat.