10 August 2013

Butterfly of the Month - August 2013

Butterfly of the Month - August 2013
The Mangrove Tree Nymph (Idea leuconoe chersonesia)

A magnificent individual of the Mangrove Tree Nymph spotted on Pulau Ubin last month

The aftermath of the haze that affected Singapore and southern Johor in the month of June appears to have created some delayed effect on the butterfly population. Although the haze has abated, perhaps due to the combination of the rains and also the Indonesian government's timely action to curtail the open burning of forests in Sumatra, the particles in the air during the height of the haze may have been fatal to the caterpillars of various stages.

Interestingly, if we tracked the average time lag between the early caterpillar instars, pupation and eclosion of the majority of butterfly species, it appears to correlate with the time that these butterflies would have eclosed in early August. All over Singapore, there is an apparent reduction in the numbers of butterflies in many areas where they are usually found. Is this a coincidence? Or really a result of the environmental damage caused to butterflies by the recent haze? Perhaps this is a study that academic researchers may want to pursue to ascertain the extent of the damage caused by the haze.

August saw the celebration of Singapore's 48th birthday on 9th, as the Muslim community also celebrated Hari Raya Puasa a day earlier. The long 4-day weekend is a much welcomed break for many, although ButterflyCircle members' outings in Singapore seemed to re-affirm the low butterfly activity across the island. It is hoped that our winged jewels will spring back again in numbers, as they have been doing so in past years.

We feature the very rare Mangrove Tree Nymph (Idea leuconoe chersonesia) as our Butterfly of the Month for August. This species was first re-discovered on the military training island of Pulau Tekong in the early 2000's during an NParks survey of the island. Subsequent trips indicate that there was a small but highly threatened population of this large Idea species in the mangrove areas on the north of the island. Since then, there were some unconfirmed sightings of the species in the neighbouring island of Pulau Ubin.

The Mangrove Tree Nymph feeding on the flowers of the Peacock Flower bush

Late last month, during a ButterflyCircle outing to Pulau Ubin, members spotted a large black-and-white butterfly flying slowly and feeding on the Peacock Flower (Caesalpinia pulcherrima). It was confirmed to be the Mangrove Tree Nymph! The large individual, which appeared to be a female, was flying up and down, teasing our members who were trying hard to get a good shot of it. After feeding at a few flowers, it decided to take refuge in the shaded forested area nearby, and rested a few times. We continued following it until it decided to move off elsewhere and flew high above the treetops and out of sight.

The Mangrove Tree Nymph soaring high in the air

It was indeed exciting to see the Mangrove Tree Nymph after so many years, and we hope that it is successfully breeding in the mangrove areas of Pulau Ubin. The caterpillar host plant is probably one of the lactiferous plants of the Apocynaceae family. It would be great if the life history could be recorded before this species disappears from its preferred mangrove habitats that is progressively disappearing from Singapore and Malaysia.

The Mangrove Tree Nymph is a large butterfly, with a wingspan usually exceeding 130mm and often reaching 150mm or more. It displays the aposematic black and white colours like the other species of its genus. It features large black spots on both wings where the marginal and submarginal black spots are conjoined to form an irregular black band. The post-discal triangular spots on the hindwings are large and always touching the black veins, forming a jagged black band. The wing bases are yellow tinted.

The Mangrove Tree Nymph is a very rare species that occurs in coastal mangrove habitats. It is known to occur in Pulau Tioman in Malaysia and believed to also occur in the mangrove areas of Johor. A recent survey on one of the small offshore islands near the Indonesian resort island of Batam also yielded a sighting of the Mangrove Tree Nymph in the mangrove area of the island.

The Taiwan Tree Nymph (Idea leuconoe clara) shot at Sentosa Butterfly Park

The species is not to be confused with the abundant and easily bred subspecies clara that originates from Taiwan. Another possible subspecies would be siamensis that occurs in Thailand.  This subspecies (either clara or siamensis) occurs in many butterfly parks and farms across the globe and is bred for its showy appearance - popular with visitors to these butterfly enclosures.

Thus far, it has been seen regularly in butterfly parks in Penang, Kuala Lumpur, Malacca and as far north as the Phuket Butterfly Farm in Thailand. In Singapore, it is a regular "resident" species found at the Fragile Forest enclosure at the Singapore Zoo, the Sentosa Butterfly Park, Changi Airport Terminal 3 Butterfly Garden and the Hort Park Butterfly Garden.

A mating pair of the Tree Nymph shot at Phuket Butterfly Park.  Possibly subspecies siamensis?

The subspecies clara as it is known at the moment, has a whiter appearance, with the black markings on the wings reduced as compared to subspecies chersonesia. Another related subspecies, siamensis which has a similar appearance to subspecies clara also occurs in Thailand. A characteristic feature is that the post-discal spots on the hindwings, particularly in spaces 4, 5 and 6 are much reduced and not conjoined.  

Given the relative abundance of this non-native species, there is a high possibility of escapees from the various butterfly parks. Indeed, two individuals were spotted in the Sime Forest of the Central Catchment area (and captured) in 2004 and 2005. It is interesting that no escapee has been able to colonise any area in Singapore as yet. Perhaps its preferred caterpillar host plant is not available in abundance, and unable to support any succeeding generations of these escapees.

In any case, we hope that the opportune sighting of the real McCoy, the Mangrove Tree Nymph ssp chersonesia at Pulau Ubin is a good sign that the species still exists in Singapore. Though its hold on to survival is tenuous and is considered a critically endangered species, we hope that it will continue to survive in the remaining mangrove habitats of Singapore for many years to come.

Text by Khew SK : Photos by Chng CK, Goh EC, Khew SK, Loke PF, Nona Ooi, Simon Sng, Anthony Wong & Mark Wong.

Special footnote : In the Butterflies of the Malay Peninsula, it was suggested that the various subspecies of Idea leuconoe could in reality be two distinct species, due to differences in their caterpillars. In which case, the Mangrove Tree Nymph would be assigned the name Idea engania (Doherty, 1891). Until there is a definitive research and a published paper on this, the Mangrove Tree Nymph remains subspecies chersonesia of Idea leuconoe for the time being.