SOUTH AUSTRALIAN BUTTERFLIES
Data Sheet

Taractrocera anisomorpha (Lower)   (Orange Grass-dart)

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Male

Interesting aspects:  This skipper belongs to a group of skippers (Hesperiinae) that are more at home in the hot tropics and subtropics, and this skipper is no exception being found in the northern half of Australia.  The skipper, along with most others in the group, has a characteristic wing pose when settled in full sun, with the forewings being held vertical (or nearly so) while the hindwings are held horizontal.  

It should not be confused with the more common Ocybadistes walkeri.   These two skippers are differentiated from each other by the shape of the thickened antennae tips, which are spoon shaped in T. anisomorha, whereas in O. walkeri the thickened antennae tips are strongly bent or hooked.  They also occur separately in different parts of South Australia.  There is however another skipper Taractrocera ina, which also occurs in central Australia (but yet to be recorded in South Australia) that is very similar to T. anisomorpha including the spoon shaped antennae tips.   Males of the latter have a dark silvery grey sex mark situated transversely across the middle of the forewing upperside, but sex marks are absent in male T. ina.   The females are very difficult to differentiate.

The skipper flies in grassy areas and has a rapid flight.  Both sexes spend a lot of time feeding from small flowers.  Males will settle on the ground, and are also known to hilltop.  Females also fly in grassy areas, and have a slower flight when in an egg laying mode, and will periodically land on the grass to lay eggs or sun themselves, and will cover large areas looking for suitable grassy habitat to lay eggs.  The skipper is timid, but can be approached with care when settled, especially when feeding at flowers, although once in full flight they are very quickly lost to sight due to their small size.

This skipper forms part of the inland endemic aridland fauna and has developed survival means to overcome the periodic extended dry periods.  Its larvae can enter into a dormant diapause condition when either the season becomes too cold over winter, or if the foodplant grass becomes too dry or rank to eat.  The larvae remain in this condition until either the following spring or summer, or when rains again fall in the region to promote new growth of the grass.  Under the latter conditions, the larvae rapidly finish off late stage larval development and pupate so that the emergent adults can take advantage of any rejuvenated green growth of their foodplant and a blossoming of nectar plants. There are records of overwintering larvae (it gets below freezing at night during winter in central Australia) remaining dormant for 9 months (May to January-in captivity), which when compared to other endemic aridland skippers (Croitana arenaria) occurring in the region, is about the maximum time they can survive without eating.

Life History

Larval food-host:  Native and introduced grasses including *Cenchrus ciliaris (black buffel grass), Enteropogon acicularis (branching umbrella grass or curly windmill grass), Eulalia aurea (sugar-grass or silky browntop), *Sorghum spp (Poaceae).  The larvae eat the leaves of the foodplant.

Eggs:  Large, domal or hemispherical shaped, base flat circular, pale yellow when newly laid.  Eggs turn white near hatching.  The small micropylar area on top of the egg is depressed, the upper part of the egg surface has a very fine indistinct raised polygonal pattern, while the lower part has indistinct, very fine vertical ridges.  The base is rimmed.  Laid singly on the leaves of the foodplant.  The egg shell is eaten by the larva after its emergence.

Larvae:  Mature final instar 18-24mm long.

Pupae:  14-16mm long, the pupal period in captivity is 11-12 days in mid-summer. 

Flight period in S.A.:  The only South Australian records are for early October.  In the adjacent areas of the Northern Territory it has also been recorded during late December-early January.  In central Queensland the skipper flies during the warm months from September to May, and the same flight period is also likely to occur in the Far North of SA.  However, the skipper probably has an opportunistic flight pattern in central Australia dependant on the infrequent rains that promote rejuvenated growth of the perennial foodplant grasses.  These rains can occur as semi-reliable light winter rains that would likely promote a regular flight in spring, and infrequent heavy thunderstorms during late spring to autumn.  During times of good rains the skipper can complete a brood in 12 weeks in late spring to early summer.  The skipper normally overwinters as larvae.

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Distribution:  This skipper has only recently been found in South Australia, where it is known to occur along several ephemeral creeks and rivers in the Far Northwest Region that have their origins in the Musgrave and Everard Ranges.  It probably has a wider distribution than presently known as the skipper is very small (bee-size) and is easily overlooked, and occurs in an area that has been poorly surveyed for butterflies.  The skipper is known to occur sporadically throughout the tropical and subtropical northern half of Australia.

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Habitat:  The skipper seems to favour open woodland habitat on the dry side.  In South Australia it is presently only known to occur along the ephemeral creek and river systems in the arid northwest of the state, where its perennial grass foodplants Enteropogon acicularis and Eulalia aurea commonly occur, and remain in a living condition throughout the year.  During good seasons, the adults probably either migrate out of the creek lines (and eventually get lost), or move up and down the creek lines following the occurrence of the foodplants. 

Conservation Status in S.A.:  It is only seen sporadically and usually occurs in low numbers at any one location, and on that basis is considered to be rare.

Threats:  The main threats would be drought, periodic floods, and the effects of pastoral disturbances through over-grazing and trampling by cattle.

Conservation Strategy:  None required.  It is likely to occur on aboriginal lands in the Far Northwest, where cattle grazing no longer occurs, and so should be reasonably protected. 

 

Author:  R. GRUND, copyright 14 July 2002, all rights reserved.
Last update 14 July 2002.