Common Imperial Blue (Jalmenus evagoras)
Adults clustering on Silver Wattle (Acacia dealbata)

Also known as the Imperial Hairstreak, this is an eyecatching butterfly with a fascinating life-history. It is one of several butterflies in Victoria that has a symbiotic relationship with certain types of ants. The ants protect the butterfly larvae/caterpillars from predators and the larvae ‘reward’, or ‘bribe’ the ants with sugary and amino acid secretions. Its a win-win, but it comes at a cost to the butterflies: the ants can live without the butterflies, but the butterflies can’t live without the ants. Read more about this Here and Here.

Common Imperial Blue (Jalmenus evagoras)
Larva with a few attendant ants

And the caterpillars only eat certain types of plants. In our region its the Silver Wattle (Acacia dealbata). So, for the Common Imperial Blue to occur in an area, it needs to have both Silver Wattles and the right species of ant (Iridomyrmex sp).

Common Imperial Blue (Jalmenus evagoras)
Pupae attached to Silver Wattle branches

Sometimes the caterpillars pupate in tight groups within an ant nest, presumably offering added protection.

Common Imperial Blue (Jalmenus evagoras)
Pupae and pupal cases attached to the underside of a branch

But pupae can also be found in single rows attached to the underside of twigs and branches.

Common Imperial Blue (Jalmenus evagoras)
An adult Common Imperial Blue, likely a male, waiting for female adults to emerge from their pupal cases.

Males often cluster around soon-to-emerge female butterflies in order to mate with them

Common Imperial Blue (Jalmenus evagoras)
Denuded branches of Silver Wattle

The two tell-tale signs of the presence of Common Imperial Blues in the Strathbogies are (1) denuded outer branches on low, regrowth Silver Wattles and (2) dark ‘blobs’ hanging from the branches.

These images were taken in the foothills of the Strathbogie Ranges, near Merton.

For a technical review about ant-butterfly relationships like this one download this 483 KB pdf Ant-associate Lycaenid butterfly – review.

Read more about the influence of ants on host plant selection in this 2.6 MB scientific paper by Pearce & Elgar.