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Imperial Hairstreak (Jalmenus evagoras)

Imperial Hairstreak

Appearance: Upperside dark grey with extended light blue areas. Underside light brown with characteristic pattern of black lines and spots. Long tail on the hind wing.
Wingspan: 3.0–4.0 cm
Season: 2–3 generations from spring until autumn.
Range: Central and eastern VIC, eastern NSW, and south-eastern and eastern QLD.
Habitat: Forest and woodland.
Photo: Male, Lane Cove NP, NSW, 08/03/2008.

Description

The Imperial Hairstreak is a common and widespread species across the temperate and subtropical areas of south-eastern Australia. The butterflies have a rather unusual lifestyle in that they spend most of their life in close symbiosis with ants. After hatching, the caterpillars feed on the leaves of Acacia plants. Through special pheromones they attract ants which permanently surround and guard the caterpillars. The adult butterflies also remain close to the larval food plants, where males can often be found resting on branches in large numbers, waiting for the opportunity to mate with freshly emerged females.

The Imperial Hairstreak appears to prefer small and young Acacia plants, and often the populated plants get stripped off their leaves by the large number of ever-hungry caterpillars. Hence, the easiest way to find this magnificent butterfly is to look out for small Acacia shrubs with a large number of ants along their branches and feeding traces on their leaves.

There are several very similar species in the genus Jalmenus, most of which are not quite as common and widespread as the Imperial Hairstreak. Usually, the Imperial Hairstreak has the light blue areas on the upperside of the wings brighter and more distinct, and the dark lines on the underside broader and more sharply defined compared to other species.

Additional Photos

Imperial Hairstreak
The upperside is dark grey with extended, light blue areas and a few subtornal orange patches on the hind wing. (Marsfield, NSW, 02/03/2008)
Imperial Hairstreak
The underside is mainly light brown with a characteristic pattern of broad, black lines. (Marsfield, NSW, 10/12/2007)
Imperial Hairstreak
Another image showing the characteristic underside. (Lane Cove NP, NSW, 31/01/2010)
Imperial Hairstreak
Males are often found sitting on the larval food plant in large numbers, waiting for freshly hatched females. (Marsfield, NSW, 09/12/2007)
Imperial Hairstreak
In contrast to similar species, the black lines on the underside of the Imperial Hairstreak are very broad and distinct. (Glenbrook, NSW, 02/04/2010)
Imperial Hairstreak
Mating pair. (Glenbrook, NSW, 02/04/2010)
Imperial Hairstreak
The tiny white eggs are attached to branches of the food plant. (Marsfield, NSW, 15/12/2007)
Imperial Hairstreak
The caterpillars are brown and often surrounded by attendant ants. (Lane Cove NP, NSW, 08/03/2008)
Imperial Hairstreak
Even the black and red pupae, usually attached to the food plant, are still attracting ants. (Ingleburn, NSW, 20/02/2011)
Imperial Hairstreak
Another image of already hatched pupae attached to the food plant. (Marsfield, NSW, 09/03/2010)