The arid bronze azure butterfly (Ogyris subterrestris petrina) is a threatened species that is listed as critically endangered under the national Environment Protection and Biodiversity Protection Act 1999 and the state Biodiversity Conservation Act 2016. The ABAB is listed due to its severely fragmented distribution with only two extant subpopulations being recorded in Western Australia. These subpopulations are at Barbalin Nature Reserve (BNR), and at a second site ~100km from Barbalin. This second site is small and its precise location is withheld for conservation reasons. A third subpopulation (the first discovered, in the 1980s) occurred near Lake Douglas, 12km SW of Kalgoorlie, but is now locally extinct and no ABAB have been recorded there since 1993..

The ABAB is a medium sized (wingspan ~36mm) robust butterfly capable of rapid flight. It is slightly smaller than the common 'cabbage white' butterfly (wingspan ~44mm). It is predominately dark grey-brown to black, with bronze to purple-bronze coloration on the upper-sides of the wings. The underside is grey-brown with iridescent bluish-white bars in the forewing cell and a series of brown-black markings on the hind wing. It is sexually dimorphic, with males having a dull dark purplish-bronze upper side whereas females have purplish areas on the upper sides of both wings and a distinctive cream patch on the forewing (Figure 1).

The ABAB has an obligate association with a sugar ant Camponotus sp. nr. terebrans. The ABAB’s larvae live entirely within the ant’s nest during their development. The ants protect the larvae from predators and are thought to be rewarded with secretions produced by the larvae. The most critical factor for habitat occupancy by the butterfly is the presence of large colonies of the host ant; only large colonies can support the ABAB because, being a parasitic species, it requires large numbers of hosts. The potential distribution is extensive and encompasses much of the semi-arid zone (rainfall < 325mm) south of approximately 26o S latitude (Map 1)

The ABAB may be identified by several distinctive features:

  1. Unique very dark colouration (adults, especially males, appear almost black in flight),
  2. A habit of perching on the ground in open areas (including on roads and roadsides),
  3. A very rapid and direct flight pattern which is characteristic of the genus, and
  4. Being amongst the largest lycaenid butterflies in Australia.

butterflies sugar ant worker
Figure 1. Left: preserved specimens of adult arid bronze azure butterflies (female at top). Right: Mature larva attended by a sugar ant worker (magnification x6). (Photos: S. Brown; T. Gamblin).

Many flowering plants of the lower, mid and upper storey are likely to be nectar sources for the adult ABAB. In woodland such as at the BNR site, many plants such as Eucalyptus, Acacia, Grevillea, Hakea, and annual species would be probable nectar plants. Nectar is likely to peak in availability during September–October, which is also the main butterfly activity (flying) period.

Eggs are laid on small stones or bark near ground level, and hatch in around 1-2 weeks. The newly hatched larvae either crawl or are carried into the ant nest. The feeding habitat for the larvae is the subterranean galleries of the sugar ant Camponotus sp. nr. terebrans. Larvae of ABAB are wholly dependent on the ants, feeding either on the immature stages of the ants or on ant regurgitations (Braby, 2000). The myrmecophilous larvae are either parasites (feeding on the ant brood) or 'cuckoos' (being fed regurgitated food by the ants). The length of the life cycle is unknown - in warmer months it may be as short as six weeks, but development time may be 6-12 months over winter.

The early stages (eggs, larvae and pupae) are difficult to detect - only two larvae and a single pupa have ever been found. The eggs are small (1.0mm diameter) and are laid in clusters of approximately 2-20 (average 8) at the base of suitable trees (i.e. those with an active ant colony). They are typically laid on the northern and western sides of the tree base, typically during the middle of the day when the ants are inactive. Hatched eggs may persist in situ for several years (Field 1999). Surveys to determine if the ABAB occurs at a site therefore rely on detecting the presence of the adult butterfly (although experienced observers may be able to locate eggs or egg cases to determine ABAB presence).

Habitat

At the two known extant sites where the ABAB occurs, the vegetation is mature mixed gimlet E. salubris/ salmon gum E. salmonophloia woodlands on red-brown loam soils, with an open understorey. In addition to gimlet and salmon gum, other smooth-barked eucalyptus at these sites which have basal ant colonies include wandooE. capilosa subsp. wandoo, smooth-barked york gumE. loxophleba subsp. lissophloia and ribbon-barked mallee E. sheathiana. The habitat at the locally extinct Lake Douglas site differs from the other sites, but is also dominated by mature smooth-barked eucalypt woodland, particularly Victoria Desert Mallee Eucalyptus concinna.

Host ant

Camponotus sp. nr. terebrans is a widespread but generally uncommon ant that occurs within inland southern Australia, including the northern and eastern wheatbelt and pastoral zone. Previously it was included in the species Camponotus terebrans Lowne, but recognised as a distinct form (the 'northern' form in McArthur et al. 1997 and the 'undescribed pale species' in Andersen 2007). It has distinct morphological and genetic differences from Camponotus terebrans sensu stricto and is now recognised as a separate species. As it has not yet been formally described as a new species, it is currently referred to as ' Camponotus sp. nr. terebrans' because of its similarity to that species. McArthur et al. 1997 give a detailed description of the host ant and this paper should be consulted to assist in identifying the ant (see https://www.publish.csiro.au/zo/ZO97055 ). Some further information is provided in Andersen (1997; p.34), and Heterick (2009) provides a key to the ant species of south-western Australia and some additional information about the species (pp.85-86).

Camponotus sp. nr. terebrans has been recorded at several sites within the semi-arid zone (rainfall <325mm), south of approximately 26o S latitude (Map 1). The ant is more common in South Australia, western NSW and north-western Victoria (where it hosts the eastern subspecies Ogyris subterrestris subterrestris). At many of the previously recorded sites in WA the ant is no longer extant – it appears to colonise a site, thrive for some years (perhaps decades), but ultimately die out. It is currently (2020) known to be extant at three large and several small colonies. Two of the three large colonies are where the ABAB also occurs. The third large ant colony is located in mixed salmon gum/gimlet woodland on both sides of Dunbar Rd (50J 0734203 E; 6481024 S), 35 km south of Marvel Loch (Figure 2. All three of the large colonies occur in mature woodland, whereas the smaller colonies are in younger regrowth (Figure 3).

one

mixed salmon gum woodland
Figure 2. Mature mixed salmon gum/gimlet woodland adjacent to Dunbar Rd (50J 0734203 E; 6481024 S), 35km S of Marvel Loch. The host ant, Camponotus sp. nr. terebrans, is common at this site and is relatively easy to detect.

gimlet woodland

Figure 3. Immature gimlet woodland (50H 0711824; 6454145) adjacent to Emu Fence Rd, 66km SSW of Marvel Loch. The host ant, Camponotus sp. nr. terebrans, occurs at this site but only in very low density and is difficult to detect.

The ant is one of the first ants to colonised disturbed areas. They make their largest nests at the base of eucalypt trees and these are sometimes apparent from a large amount of excavated soil. Workers display wide variation in size, colour, pilosity and profile, and because of this variation, major (large) and minor (small) workers may be misidentified as different species if collected away from the nest. The features and colour of the ant and its nests can be seen in Figure 4-7. As well as hosting the larvae of the ABAB, the ants also host leafhoppers ( Pogonoscopus lenis) within their nests, in another symbiotic relationship (Figure 8).

major worker intermediate worker
Figure 4. A typical major worker of Campontus sp. nr. terebrans (left) and an intermediate worker in the field. Major workers have large jaws and defend the best by biting intruders, but their bite is not dangerous to humans (T. Gamblin).

smooth barked large ant
Figure 5.
Smooth-barked eucalypt (left) and a large ant colony at the base of another eucalypt showing the large amount of excavated soil (T. Gamblin).

partly excavated partly excavated1
Figure 6. Partly-excavated host ant nest at the base of a eucalypt revealing galleries (T. Gamblin).

ant galleries any gallery1
Figure 7 . Typical features of the ant galleries below ground (T. Gamblin).

minor worker1 minor worker2
Figure 8 . Minor workers of the host ant attending a leafhopper Pogonoscopus lenis on the lower trunk of a large salmon gum in the early evening. The ant feed from the leafhopper's excretions (T. Gamblin).

Surveys for the ABAB may be required in WA where development or land management activities are proposed that could potentially affect the species and/or habitat suitable for the species. A survey guideline document has been prepared that provides guidelines for detecting current presence, or asserting the absence of the ABAB, and assessing the importance of the habitat proposed to be impacted. This can be accessed pdf Guideline for the survey of arid bronze azure butterfly1.29 MB

References and future reading

Andersen, A.N., 2007. Ant diversity in arid Australia: a systematic overview, In: Advances in ant systematics (Hymenoptera: Formicidae): homage to E. O. Wilson – 50 years of contributions . Eds. R.R. Snelling, B. L. Fisher, and P. S. Ward, pp. 19-51. Memoirs of the American Entomological Institute.

Bishop, C., Williams, M.R., Mitchell, D., Gamblin,T. 2010. Survey guidelines for the Graceful sun-moth (Synemon gratiosa) & site habitat assessments. Version 1.2 Science Division and Swan Region, Department of Environment and Conservation.

Braby, M.F., 2000. The butterflies of Australia: their identification, biology and distribution . CSIRO publishing, Collingwood, VIC.

Braby, M.F., 2016. T he complete field guide to butterflies of Australia. 2nd edn. CSIRO Publishing, Collingwood, VIC.

Department of the Environment, 2015. Conservation adviceOgyris subterrestris petrina Arid bronze azure (a butterfly) . In: Species Profile and Threats Database, Department of the Environment, Canberra.

Field, R.P., 1999. A new species of Ogyris Angas (Lepidoptera: Lycaenidae) from southern arid Australia. Memoirs of Museum Victoria 57: 251-259.

Gamblin, T., Williams, M.R., Williams, A.A.E. 2010. The ant, the butterfly, the leafhopper and the bulldozer. Landscope 21(2) : 55-58

McArthur, A. J., Adams, M. and Shattuck, S. O. (1997) A Morphological and Molecular Review of Camponotus terebrans (Lowne) (Hymenoptera: Formicidae). Australian Journal of Zoology 45 :579-598.

Schmidt, D.J., Grund, R., Williams, M.R., Hughes, J.M. 2014. Australian parasitic Ogyris butterflies: east–west divergence of highly-specialized relicts. Biological Journal of the Linnean Society 111: 473-484.

Williams, A., Williams, M. 2005. Endangered or extinct?: Kalgoorlie's arid bronze azure. Landscope 21(2): 19-23

Williams, M.R., Atkins, A.F., Hay, R.W., Bollam, H.H. 1992. The life history of Ogyris otanes C. & R. Felder in the Stirling Range, Western Australia (Lepidoptera: Lycaenidae). Australian Entomological Magazine 19: 55-60.

Williams, M.R., Hay, R.W. 2001. Two new subspecies of Ogyris otanes C. & R. Felder (Lepidoptera: Lycaenidae) from Western Australia. Australian Entomologist 28: 55-63.

Williams, M.R. and Williams, A.A.E. 2008. Threats to the critically endangered Arid Bronze Azure butterfly ( Ogyris subterrestris petrina) by proposed vegetation clearing. DEC Internal report, Nov 2008, 17 pp.

Williams, A., Williams, M., Powell, R., Walker, G. 2012. Rare butterflies of the south-west. Department of Environment and Conservation, Kensington Western Australia.