Arid Bronze Azure buttefly - east and west
For the 2020 Threatened Species Day bake-off … Here is the endangered Arid Bronze Azure butterfly in cake form.
Two populations, the Nullabour Plain in between
The are two populations of the Arid Bronze Azure butterfly. One is in Western Australia (Ogyris subterrestris petrina). When we visited Western Australia, we drove hundreds of kilometers to the Barbalin Nature Reserve (250 km NE of Perth) to visit the only known population (we didn’t see any).
Barbalin Nature Reserve October 2016
Barbalin Nature Reserve, Western Australia, October 2016
Ours is the eastern subspecies, our very own Arid Bronze Azure butterfly Ogyris subterrestris subterrestris. The Arid Bronze Azure on Raakajlim is listed under Victorian, but not federal, legislation although Braby (2000) considered both subspecies of Ogyris subterrestris to be of national conservation concern. I am told our Bronze Azure is the largest, most secure, known population of the eastern subspecies!
Arid Bronze Azure mating, the female has the larger body (Ogyris subterrestris subterrestris on Raakajlim)
Arid Bronze Azure Ogyris subterrestris subterrestris on Raakajlim
A remnant from a wetter time
The butterfly has a strange and highly specialised association with ants. They are myrmecophagous, meaning they eat ants! (well the larvae do). The butterfly relies on a single species of large nocturnal sugar ant: Camponotus terebrans. The butterfly eggs are laid near the entrance to the ant nest and the entire butterfly larval and pupal stage is completed within the nest as a predator of immature ants. The ants don’t seem to mind the reversal of the ant eats caterpillar story.
This strange caterpillar-eating-ant relationship could be a result of specialisation over evolutionary timescales. Ogyris subterrestris is an example of east-west species divergence. Our butterfly is the eastern subspecies and the critically endangered O. s. petrina (3, 4) is the matching subspecies found in Western Australia (#11 on the extinction list). The Nullabor Plain emerged as a bio-geographical barrier with the onset of aridity and throughout the Pleistocene, splitting the mesic (moister) areas into east and west. For the Arid Bronze Azure, the split occurred about three million years ago and the two subspecies have continued to evolve separately. There have been some serious genetic studies of this “phylogeographical divergence” seeking to understand how environmental change has shaped species evolution (5).
The Arid Bronze Azure are not very ”showy” but they have a distinctive wing shuffle and fly low to the ground. Sometimes the males spiral up into the air in a “dog fight”. What do we do to protect our butterfly? Because the adult butterflies are sedentary, protection of existing populations, and their host ant, is critical. We avoid soil disturbance and maintain a floristically diverse bit of bush so there are lots and lots of ants.
And 2021 Threatened Species bakeoff? - An ant cake https://www.malleeconservation.com.au/blog/an-ant-cake
Female Arid Bronze Azure caught “mid-flap” (Ogyris subterrestris subterrestris on Raakajlim)
More Ogyris information:
Arid Bronze Azure and ants - a bizarre relationship https://particle.scitech.org.au/earth/three-natures-bizarre-relationships/
Braby MF (2000). Butterflies of Australia: their identification, biology and distribution. CSIRO Publishing, Collingwood, Victoria.
DPAW (2020) Arid Bronze Azure butterfly (Western Australia) https://www.dpaw.wa.gov.au/plants-and-animals/threatened-species-and-communities/threatened-animals/562-arid-bronze-azure-butterfly
Schmidt et al. (2014) Australian parasitic Ogyris butterflies: east-west divergence of highly specialised relicts. Biol. J. Linnean Society: 111(2): 473-484. https://academic.oup.com/biolinnean/article/111/2/473/2415902 Schmidt et al. (2014) Australian parasitic Ogyris butterflies: east-west divergence of highly specialised relicts. Biol. J. Linnean Society: 111(2): 473-484. https://academic.oup.com/biolinnean/article/111/2/473/2415902
DoE (2015) Conservation Advice Ogyris subterrestris petrina Arid bronze azure (a butterfly). http://www.environment.gov.au/biodiversity/threatened/species/pubs/77743-conservation-advice.pdf
First published September 5, 2020. Updated 2021.