Small Purple Line-blue

Prosotas dubiosa dubiosa (Semper)

Interesting Aspects

This butterfly was only recently (1999) reported as being found in South Australia. It is similar in size and colour to the very common Two-spotted Line-blue (Nacaduba biocellata) and could easily be overlooked in the field for this butterfly due to the proliferation of the latter in flight. It differs from the Two-spotted Line-blue in not having the yellowish orange underside to the forewings, and by usually having only one distinctive hindwing tornal spot. However, repeated attempts to relocate the butterfly have not been successful.

The butterfly has a strong flight, but usually of short duration. Both sexes normally remain near the hostplant, although males will hilltop. The extent of the blue areas on the wings of the female is variable.

Larval Food Host

In South Australia, early stages were reported to have been found on Acacia victoriae victoriae (elegant or bramble wattle) (Mimosaceae). The butterfly will utilise the flowers of a wide variety of native and introduced plants in the eastern states that do not normally grow in South Australia. Wattle buds of many species are often utilised.

Larval Attendant Ant

Larvae can exist without ants, but are usually harmlessly associated with a few small black ants Iridomyrmex spp that forage among the wattle blossom.


Eggs are laid on the flower buds.


The mature larvae are about 8 mm long and onisciform (slater shaped), fat and strongly humped dorsally. There is a dorsal row of short blunt paired protuberances, widely spaced near the head, but gradually coming together towards the posterior end to produce a longitudinal dorsal furrow. Larvae are covered in numerous minute secondary setae. The head is small, smooth, hidden beneath the body. Yellow coloured, speckled with brown markings, the larvae closely imitate the colours of the yellow wattle blossom. The larvae remain exposed on the hostplant blossom. The larval stage lasts about 4 weeks.


Short cylindrical, smooth but with numerous short bristles, rounded anteriorly and posteriorly, the head is slightly divided anteriorly, about 6 mm long, brown coloured with darker brown markings. Larvae are reported to pupate on dead leaf debris caught in the hostplant. Attached by anal hooks and a central girdle. The pupal period is about two weeks in spring.

Flight Period in South Australia

Reported to fly in September-October in South Australia, to probably coincide with the blooming of the hostplant.

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Reported to occur at Yunta in 1999. It is not known if this butterfly is resident in South Australia or if it is a temporary occurrence due to unusual climatic conditions. The butterfly could not be found at Yunta in 2001, nor in succeeeding periods within the general area, up to the present time. The butterfly is normally found in the humid tropical and subtropical areas of Australia. It also occurs as different subspecies, throughout the tropical areas of Asia and Southeast Asia.

The butterfly may have some degree of dispersal ability (typical of the Polyommatini group of lycaenids), to account for its distribution at Yunta, and as the adult morphology is uniform in Australia.

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The Yunta habitat is open, low Acacia victoriae woodland in a semi-arid situation. The butterfly is normally found in humid tropical and subtropical woodland areas of Australia.

Conservation Status in South Australia

Probably very rare, but very little is known about its presence in South Australia. It is a common butterfly in the humid tropical and subtropical areas of Australia.


The Yunta area is a prime breeding ground for the plague locust and the butterfly would be decimated by any toxic spray programs adopted by the Locust Control Board (as happened in year 2000). The bramble wattle hostplant is very prickly and largely inedible to stock, and is sometimes treated as a woody weed in agricultural and pastoral areas, and destroyed. This hostplant also produces large seed and is presently targeted by the 'bush-tucker' industry, and the manner in which the seed is collected is fatal to any early stages of the butterfly present on the foliage of the hostplant.

Conservation Strategy

None required at this stage.