At a glance
Raakajlim is home to the largest known population of the rare Arid Bronze Azure butterfly. There are only three decent populations of this bizarre butterfly surviving in Victoria and South Australia.
The butterfly eats Sugar Ants
This butterfly is weird and a little diabolical. Neither the butterfly nor its caterpillar has a food plant. Instead, it is completely reliant on a host Sugar Ant to look after the caterpillars. Here’s what we think is happening:
The butterfly lays its eggs at the entrance to a huge Sugar Ant colony (possibly 100m across). When the caterpillars hatch they emit a chemical or pheromone. It must smell pretty good to the ants because they are tricked into taking the caterpillar into their nest. Perhaps they think it is a queen ant that needs to be looked after. But the caterpillar is secretly eating the ant babies! It spends all its time underground, predating on its host ant. In spring it emerges above ground as a beautiful butterfly.
We don’t know much about the ant-butterfly relationship
To look after this special butterfly we need to look after the ant. But we don’t know much about it. Recent genetic studies have suggested that perhaps the Sugar Ant (Camponotus terebrans) is not a single species. It might be a species complex, made up of at least seven ant species that superficially look the same. That could explain why the ant is widespread, but there are only four populations of the butterfly in the world! Perhaps the host ant is rarer than we thought?
And we don’t really know what’s going on underground in the ant nest. We’ve never managed to observe the caterpillar and ant interaction. I’m trying to establish an ant colony in my lounge room so perhaps one day I can see a caterpillar eat an ant larva. That would be cool (and of course, scientifically important).
The host Sugar Ant and butterfly eggs
The butterfly is a threatened species and has been impacted by recent flooding
The butterfly is listed as “endangered” under Victorian legislation (FFG Act). The next step is nomination as nationally threatened under the federal government’s EPBC Act. The Western Australian subspecies (Ogyris subterrestris petrina) is already listed as “critically endangered” under the EPBC Act.
In 2021, this butterfly was ranked as #7 on the list of 26 Australian butterflies most likely to go extinct in the next 20 years. Climate change & severe weather was listed as one of the four key threats to the species. Then, in December 2022, the Murray River flood spilled out onto areas of the floodplain not inundated for 50 years. We estimate that 80% of the known Victorian breeding sites for the butterfly were wiped out. The flood also impacted one of the two South Australian populations. I’m not sure the scientists
What’s it called again?
The butterfly's official, scientific name is Ogyris subterrestris subterrestris. It has a couple of common names. In Victoria, it is often called the Mildura Ogyris. This is a bit silly because it doesn’t just occur in Mildura. It’s generally called the Arid Bronze Azure butterfly. This is confusing because it shares this name with the Western Australian subspecies (Ogyris subterrestris petrina). And it’s a bit long and unwieldy.
I’m a big fan of common names that mean something and are easy to remember. I think I’d like to coin the name the Mallee Ogyris, or even better, the Underground Ogyris (subterrestris from subterrestrial - living underground). What do you think?
