21 March 2020

Lepidoptera exotica

Lepidoptera exotica : The Non-Natives
Exotic butterfly species in Singapore

An "exotic" species in Singapore, the Great Orange Tip 

Recently, I attended a workshop conducted by NParks to discuss the definitions and clarify questions about various categories that are defined in the IUCN guidelines on threatened species. The workshop was held for the team leads and assessors of the forthcoming 3rd Edition of the Singapore Red Data Book. The Singapore Red Data Book conforms to the IUCN Red List of Threatened Species but is focused specifically on Singapore's biodiversity.

The IUCN status categories in the Red List

A group of over 60 experts and taxonomic leads/assessors from academia, government organisations and the public, specialising in various terrestrial and marine groups were there to share experiences and views on the Red Data Book.  The workshop session was to help standardise how we were going to assign categories and status of the various species in our respective taxonomic areas of interest.

Some controversial categories that were debated at the Workshop

Amongst the different classifications and categories discussed, was how to consider indigenous (native) species vs exotic (non-native) species. In many cases, some of our exotic butterfly species have been "naturalised" and have established viable and sustainable colonies in Singapore. In our human world, perhaps it could somewhat be comparable to a foreigner who has lived here for many years, became a permanent resident and then took up Singapore citizenship - what is often referred to as a "naturalised Singaporean".

Another non-native species found in Singapore, the Malayan Jester

Hence do we consider "naturalised" species as native? And how long should they be "naturalised" before we take them as native? Eventually, it was decided that only native species will be assessed (irrespective of whether they are naturalised or not) while non-native species will be excluded unless they are of conservation concern, but they will be placed in a separate holding section. For the butterfly group, the question that remained was, so which species is native and which is non-native?

The Pale Grass Blue can be considered a "naturalised" exotic in Singapore, having been continuously seen in urban parks and gardens since it was first discovered in the early 2000's

Native (indigenous) is described as "naturally existing in a place or country rather than arriving from another place" or "produced, growing, living, or occurring naturally in a particular region or environment. On the other hand, a non-native (exotic) species is one that "relates to a plant or animal that is not indigenous to a region" or "an organism that living or growing in a place that is not the location of its natural occurrence."

A mating pair of Tawny Costers, an exotic that was first discovered here in 2006

Whilst the definition of native and non-native is easy to understand, the challenge is the reference baseline information. For butterflies, we have often turned to the checklists that were produced by the authors of "Butterflies of the Malay Peninsula" and "Butterflies of West Malaysia and Singapore". These checklists made reference to data from collections that dated back to the late 19th century and are used as the baseline for the definition of what species is "native' or occurred naturally in Singapore.

The Yellow Palm Dart was discovered around 2009 and is now considered common in Singapore

Let us take a look at some of these "exotic" species in Singapore, and their status based on the IUCN guidelines, if they were to be assessed. These species are deemed as non-native as they were never recorded in Singapore before, based on our reference baseline checklists.  Other than Riodinidae, all the other five families of butterflies have examples of what is non-native in Singapore.

1) The Common Jay (Graphium doson evemonides) - IUCN : Vulnerable

The non-native Common Jay was discovered in 2004, and there is a resident population on Pulau Ubin

The Common Jay was not listed in the reference checklists of the early authors and thus far, we have had no evidence of its having been captured in Singapore in the reference collections that correspond to the checklists. It was hence a "new discovery" for Singapore when it was first spotted on the offshore island of Pulau Ubin in 2004. Over the years, however, there is a sustainable colony of the species on Pulau Ubin, and continues to be seen to this day.

Given its continued presence in Singapore, the Common Jay may be assumed to be a naturalised exotic to Singapore. As it has been bred on a variety of caterpillar host plants, amongst which are Desmos chinensis, Michelia alba and Polyathia longifolia, the species has a higher chance of sustaining its existence as part of Singapore's butterfly biodiversity. However, being a non-native species, it would be excluded from being assessed for the Singapore Red Data Book 3rd Edition.

2) The Great Orange Tip (Hebomoia glaucippe arturus) - IUCN : Endangered

The Great Orange Tip is a relatively large butterfly and has a strong flight. It was recorded from Singapore near one of our reservoir parks in the early 2000's. Several reported sightings were made on the island of Pulau Ubin in subsequent years. The sightings of this non-native species were probably of vagrant individuals that made it south to Singapore carried over by prevailing winds.

The Great Orange Tip is also a feature species in butterfly parks and individuals seen in Singapore could also have been escapees from these aviaries. This non-native is rarely seen in recent years, and will not be assessed for the Red Data Book 3rd Edition.

3) The Tawny Coster (Acraea terpsicore) - IUCN : Least Concern

First recorded as a new discovery to Singapore in 2006, the Tawny Coster is common here today, and continues to be seen regularly in urban and suburban areas. It has several alternative caterpillar host plants, and is hence able to maintain a sustainable population in Singapore for the past 14 years. It is also considered naturalised and is part of our urban biodiversity in Singapore.

The exotic Tawny Coster is now a naturalised species in Singapore, where it is common in urban areas

This slow-flying species is known to be distasteful to predators and that adds to its tenacity to survive and thrive in Singapore. Another naturalised species, the non-native Tawny Coster is likely to stay for the long term and has even widened its range to as far south as Australia in recent years.

4) The Malayan Jester (Symbrenthia hippoclus selangorana) - IUCN : Endangered

A small colony of the Malayan Jester survived at the Dairy Farm Nature Park for some time.

An individual of the Malayan Jester was first recorded as a new discovery for Singapore when it was spotted in 2012. The species was considered a possible vagrant until in the past 3-4 years when a colony established itself at the Dairy Farm Nature Park area. Whether the population can be sustained to qualify this species as a naturalised species remains to be seen.

Unlike other non-native species that have become common in Singapore, the appearance of this species has been erratic. However, where it occurs in Malaysia, the species is not uncommon. However, its appearance in Singapore would classify it as a non-native species and will not be assessed for the Singapore Red Data Book 3rd Edition.

5) The Pale Grass Blue (Zizeeria maha serica) - IUCN : Least Concern

This small butterfly was discovered here in the early 2000's, and was validated by the late Col John Eliot. The species was included in his Malayan Nature Journal : Update to C&P4 paper. The species has been considered extant in Singapore since the early 2000's and continues to be found here as a relatively common species. An individual was photographed at the Bt Panjang Butterfly Garden as recently as last weekend.

This naturalised species is relatively common, and in areas where they fly, there can be as many as 6-12 individuals fluttering around the grasses and wild flowers. Its caterpillar host plant, the Yellow Sorrel (Oxalis corniculata) is a common "weed". The Pale Grass Blue would be considered as "Least Concern" under the IUCN guidelines, but is still classified as a non-native species in Singapore and will not be assessed in the Singapore Red Data Book 3rd Edition.

6) The Yellow Palm Dart (Cephrenes trichopepla) - IUCN : Least Concern

A species that is more associated with the Australian region than Southeast Asia, this species first appeared in 2009 in Singapore. Since then, it has also moved northwards and has been spotted in West Malaysia. The fact that the common coconut palm (Cocos nucifera) is its caterpillar host plant may explain its rapid spread across the region.

This exotic species has now become common and is regularly seen at urban parks and gardens where the coconut palm can be found. It was even recorded from the offshore island of Pulau Semakau during our surveys conducted for the National Environment Agency on the island.

Participants at the Red Data Book 3rd Edition Workshop organised by NParks

And so, here we see a small sample of the exotics or non-native butterflies of Singapore. Some have become naturalised and common, whilst others continue to be elusive or probably vagrants. There are many other species that are exotic to Singapore, and they will not be assessed and featured in the main section on butterflies in the Singapore Red Data Book 3rd Edition.

Text by Khew SK : Photos by Khew SK, Loh MY, Jonathan Soong and Anthony Wong