Jalmenus evagoras

Jalmenus evagoras (Donovan, 1805)
Common Imperial Blue
ZESIINI , THECLINAE , LYCAENIDAE

Don Herbison-Evans ( donherbisonevans@yahoo.com )
and
Stella Crossley & Will Douglas (Burra Creek, Moruya, NSW)

(updated 16 June 2009)

The eggs of this species are white or pale green, and ridged with little spikes. They have a diameter of about 0.6 mm. The eggs are laid in rows on the stems of a foodplant. Initially the caterpillars are orange, and they wander around looking for an ant trail. They then follow this hopefully to find a cluster of older caterpillars.

(Photo: courtesy of Merlin Crossley)

The Caterpillars are flattened and have fleshy spiky dorsal tubercles on most segmemts. They are coloured dark green with an orange dorsal line and other lighter markings. They feed communally in a web on the foliage on various Wattles ( Acacia, MIMOSACEAE ) such as:

Sally ( Acacia falcata )

Mudgee Wattle ( Acacia spectabilis ).

The host is invariably a juvenile bush under 2 metres tall. The Caterpillars always attended by swarms of black ants from the subfamily DOLICHODERINAE, including :

Iridomyrmex anceps, or

Iridomyrmex rufoniger.

These ants have been observed defending the caterpillars from predators such as mantids and spiders. A good way of locating the caterpillars is to follow ants as they run along the branches of potential foodplants. David Lohman has discovered that only three species of ants associate with the Caterpillars, other species of ants attacking and killing the Caterpillars. The Caterpillars grow to a length of about 2 cms.

They pupate communally in their web, amongst the foliage of the foodplant. The individual pupae are black and shiny, with orange between segments. Communication between Caterpillars and between pupae has been studied by Mark Travassos and Naomi Pierce at Harvard. The pupae have a length of about 1.3 cms.

(Photo: courtesy of Martin Purvis, Ingleburn, NSW)

The adult is metallic blue in colour with black wing margins. A small black bar occurs at the end of the cell on each fore wing. Each hind wing is extended into a black tail, and is decorated with two orange spots and some thin white lines. The undersurfaces of the wings are creamy fawn, marked with black lines of various lengths. The undersides have black termens with pale orange-brown subterminal bands, and bright orange patches to mark each tornus.

(Specimen: courtesy of the The Australian Museum)

The coloured tails of the butterfly look like white-tipped antennae on bright red/orange and black colourings which, with wings folded (the habitual posture) makes the back end of the butterfly look like the front end (the actual head and antennae being quite bland). This is perhaps a decoy perhaps in case of bird strike.

(Photo: courtesy of Martin Purvis, Ingleburn, NSW)

The wingspan is about 4 cms. The adults are seldom seen more than 20 metres from a foodplant, and are inclined to congregate around the foodplant, so are easily detected this way.

In Melbourne in December and January, we have found eggs and Caterpillars and pupae and adults on the same bushes at the same time. There appear to be two generations per year in Melbourne, with the later generation overwintering as eggs, and hatching the following spring. The reproduction of the species has been studied by Diane Wagner et al and Lesley Hughes. Two subspecies have been recognised in south-eastern Australia :

eubulus in southern Queensland, and

evagoras in New South Wales and Victoria.

The distribution has been studied by John Smiley and Peter Atsatt.