Imperial Blue


Imperial Blue - Jalmenus evagoras


This page contains information and pictures about Imperial Blue Butterflies in the Brisbane area, Queensland, Australia. The butterfly also known as Imperial Hairstreak.

Wingspan 40mm
The Imperial Blue butterflies are brownish blue on the top side and pale yellow with black lines on the underside. There are long curled tails on each hind wing. Females lay eggs on different kinds of wattles. They are locally common in Brisbane eucalypt forests, seldom seen far away from host plants.
wpe3.jpg (33094 bytes) wpe1.jpg (21847 bytes)
The top view of the open-winged butterfly look like the face of a cat, hold prey with its bloody mouth. This pattern will scare most of the birds - the butterfly's predator. About this point, we have detail discussions in this page.
wpe5.jpg (25725 bytes) wpe3.jpg (39800 bytes) PWC_8369.jpg (175609 bytes)
Males and females looked very similar, quite hard to distinguish on photos.    
PWC_8386.jpg (142798 bytes)

Males cluster around pupae

wpe1.jpg (35280 bytes) DSCN6467.jpg (136389 bytes) DSCN6463.jpg (147659 bytes)
Males cluster around pupae waiting for the emerge of females.  
PWC_8373.jpg (142122 bytes) wpe6.jpg (25205 bytes)  
During a sunny summer day, the male butterflies are found flying around the host plants, waiting to mate with females.
PWC_8372.jpg (160190 bytes) PWC_8396.jpg (174114 bytes) PWC_8366.jpg (181217 bytes)

Eggs, Caterpillars and Pupa

The eggs of this butterfly are white to pale green in colours. The eggs are laid in rows on the stems of food plant. Female will lay eggs on different type of wattle, however, she will only choose the wattle with the right type of ants colony.
DSC_3058.jpg (179191 bytes) DSC_3063.jpg (183626 bytes) DSC_3066.jpg (162946 bytes)  
The caterpillars are quite common on Wattle Acacia leaves. They can easily be found during summer on the day time feeding on the leaves. The caterpillars and pupae are always attended by ants
DSC_3778.jpg (161793 bytes) DSC_3779.jpg (175328 bytes) DSC_2588.jpg (126828 bytes)
wpe2C.jpg (17653 bytes) wpe34.jpg (21534 bytes) wpe1.jpg (23536 bytes)
Caterpillar 40mm                                                  The caterpillar about to turn into a pupa   
The caterpillars secrete a substance which the ants like. It is believed that the ants will provide protection from predators and parasitism as return. This is why the caterpillars can feed freely during the day time. The caterpillars usually pupate in group on a communal web spun among twigs.
DSC_0045.jpg (183685 bytes) DSC_0050.jpg (211766 bytes) DSC_2142.jpg (137816 bytes)   
Imperial Blue caterpillars feed openly during the days.
PWC_9088.jpg (115436 bytes) wpe1B.jpg (31919 bytes)
Caterpillars pupate together in group on web of silk that they build between branches and leaves of host plants.

Raised Imperial Blue at Home

We striped the ants away and collected two caterpillars, raised them in a jar with some fresh Wattle leaves. Without the ants protection in the wild, scientists had shown that the caterpillar will subject to parasite or predation within days.
wpe36.jpg (25582 bytes) wpe38.jpg (23874 bytes)
A few days later, the two caterpillars turned into pupa. The two caterpillars pupated close to each others. The Pupa are dark brown in colour.
We know that for some other blue butterfly species, the caterpillars hind during the day and rely on the ants to guide them to the food plants. This Imperial Blue caterpillar seemed living fine without those ants About a week later, the Imperial Blue butterflies came out from the pupa.

Attended by Ants

Their caterpillars and pupa are always found attended by ants. In return for protection from predators and parasites, the caterpillars provide secretions that the ants find nutritious. Caterpillars feed on many types of Acacia as host plants. However, females will only lay eggs on host plants that have the right species of Ants. 
DSC_3778.jpg (161793 bytes) DSC_3774.jpg (215167 bytes) DSC_3048.jpg (176543 bytes)
Some reference books suggested that the ants come for the honey dew produced by the special secretary organs on their body. 
DSC_3779.jpg (163079 bytes) wpe17.jpg (24957 bytes) wpe1B.jpg (31919 bytes) 
However, we noticed that the ants also attended the pupa, which were not likely to produce any honey dew. The Caterpillars always attended by the ants Iridomyrmex sp. from the subfamily DOLICHODERINAE and not by other species of ants. We suspected that the caterpillar and pupa may exploit and take the advantage the chemical signals of those ants. The caterpillar and pupa may secrete the chemical so that the ants think they are their 'Queen' or 'sisters'. This is just a speculation that need more observations to confirm.

Host Plants - Wattles

wpe4.jpg (26050 bytes) DSC_1379.jpg (172636 bytes) DSC_2828.jpg (129548 bytes)
Caterpillars feed on many types of Acacia as host plants. However, females will only lay eggs on host plants that have the right species of Ants. The wattle trees selected are usually medium size young trees, about two meters high, which are in group within a small area. The wattles are those common species include Acacia leiocalyx, A. harpopylla, A. irrorata, A. melanoxylon, A. mearnsii. 
DSC_2141.jpg (141866 bytes) PWC_9089.jpg (168370 bytes) DSC_0049.jpg (141897 bytes)  


DSC_2583.jpg (147452 bytes) 
Without the ants protection in the wild, scientists had shown that the caterpillar will subject to parasite or predation within days.

1. Insects of Australia, CSIRO, Division of Entomology, Melbourne University Press, 2nd Edition 1991, p 899.
2. Insects of Australia and New Zealand - R. J. Tillyard, Angus & Robertson, Ltd, Sydney, 1926, p465.
3. Create More Butterflies -  by Frank Jordan and Helen Schwencke, Earthling Enterprises, 2005, p22.
4. Jalmenus evagoras - Australian Caterpillars, Don Herbison-Evans & Stella Crossley, 2009.
5. Flying Colours, Common Caterpillars, Butterflies and Moths of South-Eastern Australia - Pat & Mike Coupar,1992, p99. 

Back to Top

Up ]


See us in Home page. Download large pictures in Wallpaper web page. Give us comments in Guest Book, or send email. A great way to support us is to buy the Brisbane Insects and Spiders CD.  
Last updated: July 20, 2010.