06 March 2008

Voyage of the Tawny Coster

The Voyage of the Tawny Coster (Acraea terpsicore)

Some time back in 2006, a member of ButterflyCircle, Rey Aguila, photographed a mating pair of orange coloured butterflies which he thought were moths. Upon seeing the posted shot, we immediately knew that the Tawny Coster had finally completed its long voyage to Singapore, which started in India and Sri Lanka - a journey which probably took over three decades to complete.

ButterflyCircle members went to the open patch of wasteland to investigate where the pair was first sighted, and found to our pleasant surprise, a colony of the Tawny Costers at the site. Fluttering effortlessly in the breezy area were a good number of males and females of this new addition to the Singapore checklist. They had finally arrived in Singapore!

The Tawny Coster is known to be common in India and Sri Lanka, where it can be found both in forest clearings and open country. Though mainly seen at low elevations, it has been recorded at heights of up to 7,000 ft in South India and sometimes in the north.

Tracing the route of this new species for the region, we found documentary evidence of the appearance of this species in Thailand in the early 80's. How long it had taken to move over land from India and Sri Lanka past Bangladesh, Myanmar and finally to Thailand, is anybody's guess. But it was already a resident species in Thailand by the early 80's.

Sporadic sightings were recorded in South Thailand and the northern part of West Malaysia, and a confirmed record specimen was collected by Arshad at the edge of the Batu Pahat forest reserve in Perlis in 1992. Another sighting was made by Wong Tet Seng in early 1993 near Tanjung Rhu on Pulau Langkawi and subsequently on open land in Bukit Mertajam in the northern state of Penang in April 1993.

It was also recorded on Penang island in that year. Sightings of the species in the remaining years of the 90's were scattered and undocumented. It appeared in 2002 in Petaling Jaya, and was photographed by a butterfly enthusiast. A further sighting was recorded in 2003 in Negri Sembilan.

No further documented records of the sighting of the butterfly were found until 2006 when it appeared at an open wasteland in the north-eastern part of Singapore island. It spread across the island and has become a rather common species all over Singapore, including the offshore island of Pulau Ubin.

A further bonus sighting of the butterfly by veteran nature guide, Subaraj Rajathurai, was made on the Indonesian island of Batam, immediately after it was observed in Singapore.

The Tawny Coster (Acraea terpsicore)

The Tawny Coster belongs to the family Nymphalidae ; Subfamily Heliconiinae. The butterflies of this subfamily are characterised by a perfectly flat hindwing and by having the cells of both wings closed by tubular veins. Their behaviour is sluggish, and, like the Danainae, they have a leathery body and are tenacious of life. They frequently exhibit Mullerian mimicry and serve as models for Batesian mimics from other families. The subfamily is strongly represented in the Ethiopian region, less so in the Neotropical Region, and is weakly represented in the Oriental and Australiasian Regions.

The egg resembles that of Danaini being much higher than wide and bearing rather ill-defined vertical ribs. The eggs are laid in clusters and the gregarious larvae are cylindrical and bear branched spines, termed scoli, on each segment. The host plants are commonly species of Passifloraceae.

The female Tawny Coster typically oviposits a large clutch of eggs numbering anywhere from 20 to 50 eggs in one sitting. The eggs are carefully arranged on the undersides of a leaf of the host plant. In Singapore, the species has adapted itself to the host plant Passiflora foetida. This host plant, a common "weed" growing in wasteland and cleared open areas, is a fast-growing vine.

The relatively plentiful availability of the host plant could be one of the reasons for the rapid spread of the Tawny Coster across Singapore. Furthermore, as each clutch of eggs hatch, the large numbers of caterpillars would make the species more likely to succeed in colonising areas where the host plants are abundant. As the Tawny Coster is distasteful to predators like birds, this also gives it a better chance of survival.

The upperside of the Tawny Coster is a deep orange in the male and a lighter orange-yellow in the female. There is a transverse black spot in cell, and another irregular, oblique and broader at the disco-cellulars. The upper four spots of the discal series inclined obliquely outwards, the lower two obliquely inwards The hindwing possesses a basal series of four or five black spots with a similar spot beyond in middle of cell and a subcostal black spot above it, followed by a discal series of obscure blackish spots.

The underside ground-colour is ochraceous yellow or a paler tawny yellow. The forewing paling to whitish on the apex, with the black markings as on the upper side but somewhat blurred and diffuse. The hindwing has a series of white spots traversing the black terminal margin. Antennae black, head and thorax black spotted with ochraceous and white.

The Tawny Coster has a wingspan of 53-64 mm.

The caterpillars are cylindrical, slender, with six longitudinal rows of fine branched spines; colour reddish brown with an oily gloss, much paler on the head, second and last segment. The pupa is perpendicularly hung, long, slender, smooth; two lateral angles on the thorax; head quadrate; colour creamy white, with broad longitudinal bars of purplish-black spotted with orange.

The Journey South is Complete
How this tenacious butterfly is able to slowly but surely make its voyage down all the way to Singapore from its origins in India and Sri Lanka is one of the wonders of the natural world. Using its ability to feed on a variety of host plants in the families Passifloraceae and Loganiaceae and probably a number of others, it has leapfrogged over land and survived predators and other dangers to cover a distance of many thousand kilometres to end up in Singapore.

Having now also been seen in Batam, it will surely try to continue its journey to Bintan in the Riau Archipelago, and who knows whether it will appear in the main Indonesian islands one day in the not too distant future?

But for now, Singapore has a new resident species - and a pretty and colourful butterfly at that, and this new "foreign talent" is likely to stay with us and be a part of the diverse flora and fauna of our little island in the sun.

Text and Photos by Khew SK

References :

  1. Wikipedia : Acraea terpsicore
  2. Malayan Naturalist (Magazine of the Malaysian Nature Society) Vol 49 No 3 : 1996
  3. The Malayan Nature Journal Vol 59 Part 1 October 2006
Post Note : Various lepidopterists in India are still debating on the actual scientific name of the Tawny Coster, preferring the precedent name of Acraea terpsicore to the more recent name Acraea violae. The jury is still out on the final name. For the time being, we have kept to the more commonly used scientific name of Acraea violae based on the more popular global references of Lepidoptera.

Update 2015 : The scientific name of this species has been adopted as Acraea terpsicore by several authors henceforth, and updated accordingly.