30 August 2020

A New Discovery for 2020!

A New Discovery for 2020!
Featuring the Swamp Tiger (Danaus affinis malayanus)

A new discovery to Singapore, the Swamp Tiger

Our Saturday morning outing to Ubin started rather gloomily. The weather, that is. Even at breakfast before the boat ride over to Pulau Ubin, the skies looked threatening and the forecast predicted rain in the late morning and early afternoon. But not to disappoint our two newbies in the group, we decided to take the risk and headed off to our favourite biodiversity-rich idyllic island.

The overcast morning from Pulau Ubin Jetty

View to Pekan Quarry from Butterfly Hill - dark clouds above!

Perhaps it was due to the weather, but at least there wasn't a long queue at the ferry terminal and we made it to our boat ride after a short wait. We headed straight to Butterfly Hill, as it did not look as though the weather would stay rain-free for too long. Butterfly activity was low, and we did not see too many of the familiar species that usually roam freely on Butterfly Hill.

At the Leea shrubs, I spotted something that initially looked like a Black Veined Tiger, but it looked strange. It flew away before I could take a shot of it, and I thought that it looked like something that I had seen many years ago up north in Malaysia, but I left it as another unsolved mystery as it disappeared over the tree tops and out of sight.

The female Swamp Tiger perches on a leaf

The group went chasing after another new species that was recently re-discovered on Ubin, the Orange Gull (Cepora iudith malaya). Our newbie butterfly shooter, Gavin, had spotted something different, and called out to the rest to wait for the elusive butterfly to come down lower for a better shot. It appeared that there was more than one individual of the Orange Gull, and the overcast weather appeared to make it more lethargic than usual, and it stopped to rest more often.

We then met our prolific butterfly shooter, Michael Soh, who was, coincidentally one of those who shot the Orange Gull some months back, also on Ubin. Our "butterfly whisperer" who has been discovering rather interesting and rare species, I saw Michael shooting something amongst the bushes and joined him. It was then I instantly recalled the Danainae that I had seen earlier in the morning. This time, it was perched on a vine and readily recognisable as the Swamp Tiger (Danaus affinis malayanus)!

The Swamp Tiger (sometimes also called the Mangrove Tiger or Malay Tiger) is very restricted in distribution, and is limited to coastal areas and associated with mangrove swamps where its caterpillar host plant, a milkweed vine, Ischnostemma selangorica grows. The nature park at Kuala Selangor in Malaysia (which is more well known for its fireflies), is the place to go to see this species. There are a few other locations in Malaysia where it may be locally common, primarily near mangrove habitats. It has not been recorded from Singapore before.

The Swamp Tiger superficially resembles the Common Tiger and Black Veined Tiger of the same genus, but is generally smaller in size. It is readily distinguished by the dark orange wedge-shaped post-discal spots on the underside of the hindwing, giving it a different appearance from its other two cousins. Where it is found in Malaysia, the species is rather fast-flying and alert, and usually staying close to the ground, feeding on flowering plants like Sea Ox-Eye and Indian Camphor Weed.

A upperside shot of the Swamp Tiger

The Swamp Tiger that we spotted today was a female, and was earlier feeding at almost tree-top level, on the flowers of the Bandicoot Berry (Leea indica). It somehow came down to rest with its wings folded, and perched for a while before flying up and disappearing over the treetops again. A chance shot showing the side profile of the abdomen of this female indicated that she is likely carrying eggs. Hopefully, she is able to find a suitable host plant to lay her eggs on.

The rather large abdomen on this female Swamp Tiger suggests fertile eggs that will hopefully yield a next generation of this species on Ubin?

It is not often that we get to add one of the larger and conspicuous species of butterflies to our Singapore Butterfly checklist. The Swamp Tiger we spotted today, was probably a stray from somewhere in the mangroves of Johor, but we hope that with better conservation of the nature areas in Singapore, there will be an opportunity for more species from neighbouring countries to colonise and breed successfully.

An article on the Swamp Tiger in the Malaysian Naturalist, the newsletter of the Malaysian Nature Society

The National Parks Board's nature conservation initiatives on Pulau Ubin, with an objective of enhancing Singapore's biodiversity is reaping some success with the appearance of interesting species like the Angled Castor, Common Jay, Orange Gull, Yellow Streak Darter, Wanderer and many more. And today, we welcome one more species to Singapore - the Swamp Tiger!

Text by Khew SK : Photos by Gavin Chan, Federick Ho, Khew SK, Lim CA, Loh MY, Low SC and Michael Soh

23 August 2020

Three Eggflies

Three Eggflies
Featuring the Eggfly butterflies in Singapore

A typical male Great Eggfly (Hypolimnas bolina bolina)

The genus Hypolimnas is represented by three species in Singapore. Called by their curious English common name of "Eggfly", it would be interesting to find out how this common name was coined by the early collectors in the region. A quick search on the internet offers one possible suggestion - that the name refers to the white egg-shaped circles on the wings of the males of the species.

A male Danaid Eggfly (Hypolimnas misippus misippus) shot in Taiwan

A male Jacintha Eggfly (Hypolimnas bolina jacintha). Note the row of submarginal white spots on the wings

The species of this genus are known to be highly variable and even amongst some of the named forms, there is a wide range of intermediates across the individuals. Of the three species, two are relatively common and widely distributed across different habitats in Singapore, whilst one is very rare and, thus far, only makes its appearance, at the Southern Ridges Parks. Each of the species has unique characteristics and behaviour, and this will be discussed below.

1) The Malayan Eggfly (Hypolimnas anomala anomala)

A typical f-anomala Malayan Eggfly uppersides

The Malayan Eggfly can be considered common, although usually encountered singly and is widely distributed in Singapore across various habitats. It is often mistaken for one of the Danainae "Crows" of the Euploea genus. However its flight characteristics and habit of returning to its favourite perch after being disturbed, would give a clue as to its identity.

A form-anomala variant with blue-shot forewings

A typical form-anomala with all-brown wings

A typical form-nivas Malayan Eggfly with whitened hindwings

Malayan Eggfly form-nivas with broad white streaks on the hindwings

An intermediate Malayan Eggfly form-anomala with reduced white streaks on the hindwings

Malayan Eggfly form-anomala with all-brown hindwings

The Malayan Eggfly is dark reddish brown above, with a series of post-discal and sub-marginal white spots on both wings. The underside is darker and has similar markings as its upperside. The species is quite variable and there are two main forms flying in Singapore - the typical (and more common) form-anomala and the rarer form-nivas which has diffused white post-discal streaks on its hindwing. Occasionally, examples with a prominent blue gloss on the upperside of the forewings occur, which resembles the male Striped Blue Crow.

A female Malayan Eggfly stands guard over her clutch of eggs

One of the interesting observation of this species is that a female can lay in excess of a hundred eggs on a single leaf of its host plant. It is then observed to stand guard over the eggs until the end of her life. There was a report of a sighting of a dead female still standing guard over her eggs even after the caterpillars hatched and moved away - a very bizarre behaviour for a butterfly!

2a) The Great Eggfly (Hypolimnas bolina bolina)

A typical male Great Eggfly puddling

The species Hypolimnas bolina occurs in Singapore and Malaysia in two subspecies - the Great Eggfly (ssp bolina) and Jacintha Eggfly (ssp jacintha). The males of both subspecies look very much alike, except perhaps the underside hindwing submarginal white spots are very much reduced in ssp bolina but is wider and more distinct in ssp jacintha. Both subspecies are considered common and are widely distributed in Singapore.

Great Eggfly female form-nerina

Great Eggfly female form-alcmene

Typical underside view of a Great Eggfly.  Note the submarginal crescentic white markings

There are several named female forms of the Great Eggfly, of which the most typical form is nerina with its orange dorsal patch on the forewing above. However, the various forms are so variable and connected by a spectrum of intermediates, it is often difficult to classify the forms definitively from the physical attributes of the individuals.

A mating pair of Great Eggfly, shot at Pulau Ubin in Singapore

From field observations, although the two subspecies are currently separated, it is stated in Butterflies of the Malay Peninsula 4th Edition that "from about 1970 onwards, subspecies jacintha has partially re-established itself, where it now interbreeds with subspecies bolina giving rise to adults showing a wide degree of intergradation, such that it is often not possible to assign specimens with one subspecies or the other."

2b) The Jacintha Eggfly (Hypolimnas bolina jacintha)

A female Jacintha Eggfly showing its uppersides

As mentioned above, the ssp jacintha has certain physical characteristics that was initially more distinctive where it could be separated from ssp bolina. The most diagnostic of which is the sub-marginal "M-shaped" white spots on the underside of the hindwing. In typical examples, these spots are larger and almost form a wide band on ssp jacintha whilst they are smaller and separated in ssp bolina. However, over the years, observations of individuals where these markings are somewhat in-between have occurred, making it difficult to decide which subspecies it is.

Various variants of the female Jacintha Eggfly.

Whilst the male has a similar appearance to ssp bolina, there are new forms of ssp jacintha that appear from time to time. These new forms have generally not been described, or, with the interbreeding with ssp bolina, they may form further intermediate forms that are so highly variable that it is not even assigned a name due to the irregularities of occurrence.

Different individuals of typical undersides of the Jacintha Eggfly. Note wider submarginal white spots

A unique variant of the Jacintha Eggfly without any post-discal white patch on the hindwing

Further research and observations are certainly required of these two subspecies. Evolution of the species/subspecies is certainly still very much in progress, and it may be a matter of time before one or the other subspecies may disappear. Having the reputation of being "the most variable butterfly in the world", it will not be surprising if the evolution continues and more interesting surprises abound in the future.

3) The Danaid Eggfly (Hypolimnas misippus misippus)

A male Danaid Eggfly photographed at Mt Faber Park in Singapore

The last of the Eggfly species is the very rare Danaid Eggfly. Although listed as "extant" in Singapore by the early authors (and hence is a native species), sightings of this species have been far and few in between. Where it has been spotted over the past two decades, only males have been seen. And they usually appear for a few days at the Southern Ridges parks like Mt Faber and Telok Blangah Hill Park and totally disappear for many years.

Another male Danaid Eggfly, also shot at Mt Faber Park

The upperside of the Danaid Eggfly somewhat resembles the Great Eggfly, but the white "egg" patches on the upperside of the wings are much larger in the male. On the underside, the white discal patch is more extensive and there is a black costal spot which is absent from the Great Eggfly.

A female Danaid Eggfly shot in Taiwan.  It mimics the Plain Tiger for protection

The most interesting aspect of this species is the female, which is almost an exact replica of the Plain Tiger and flies like the Danainae. In the field, it is often wise to take a second look at anything that looks like the Plain Tiger as the female of the Danaid Eggfly has not been reliably seen nor photographed in Singapore yet.

Text by Khew SK : Photos by Khew SK, Koh CH, Loh MY, Bobby Mun, Neo TP, Nelson Ong, Michael Soh, Jonathan Soong, Tan BJ and Horace Tan

16 August 2020

Variation or Form?

Variation or Form?
Observation Notes on 3 Singapore Butterflies

A Common Tit puddles on a small stone.  The forewing is grey and weakly shaded with ochreous brown along the termen

In an earlier discussion on dimorphism and polymorphism in butterflies, we saw that in some species of butterflies, one or both sexes occur in two or more discontinuous forms due to a difference in their genetic constitution. Unlike seasonal forms (which are uncommon in Southeast Asian butterflies) which are physically differentiated primarily due to environmental factors, the forms that are caused by genetic variation are called morphs and usually given separate names.

A male Colour Sergeant perches on a leaf in a sunlit spot.  Note the orange subapical spot on the upperside of the forewing

The more obvious species that are dimorphic or polymorphic in either the males or females are well documented. Some examples are the Common Mormon (Papilio polytes romulus), of which the females occur in two forms, the Plain Tiger (Danaus chrysippus chrysippus), which occurs in two forms, and the Malay Baron (Euthalia monina monina) in which the male occurs in at least 3-4 different forms.

A female Blue Pansy with the typical brown hindwing colour

With observations over the past 3-4 decades of butterfly watching in Singapore, there are a few species that warrant closer observations for potential dimorphism. Although undocumented, these species may be good subjects for scientific research as to whether the regular variations observed suggest the possibility of a divergence in the physical characteristics of the species such that they may be considered dimorphic. These species are discussed below :

1) The male Colour Sergeant (Athyma nefte subrata)

A male Colour Sergeant with orange subapical spot.  This individual was photographed at Mt Faber Park

Sexual dimorphism is well documented in the females of the Colour Sergeant where the females occur in two distinct forms - the orange coloured form-neftina and the brown coloured form-subrata. That the females of the species occurs in two different forms is not in doubt. However, observations of the males of the Colour Sergeant poses some questions about the consistent variation (albeit a subtle one) in the colour of the subapical spot on the upperside of the forewing.

A male Colour Sergeant with white subapical spots on the forewing.  This individual was photographed at Telok Blangah Hill Park

A male Colour Sergeant with orange subapical spots on the forewing.  This individual was photographed at Ulu Sembawang Park Connector

The typical male, as described, is rich velvety black with the white markings tinged with bluish. The apical spot in space 6 of the forewing is usually white, but individuals have been recorded here in Singapore where this spot is more than just "tinged with orange". In some examples shown here, the spot is quite large and distinctly orange - even in bred specimens.

A male Orange Staff Sergeant (Athyma cama gynea) with orange subapical spots on the forewing.  This species is not found in Singapore and prefers montane habitats.

A newly-eclosed bred male Colour Sergeant with orange subapical spots on the forewing

A male Colour Sergeant with white subapical spots on the forewing.  This individual was photographed at Telok Blangah Hill Park

The variation of this subapical spot ranges from totally white with no trace of orange, to almost orange, with a range of variations in-between. This is contrasted with the similar-looking Orange Staff Sergeant (Athyma cama gynea) which is montane and does not occur in Singapore, where the subapical spot is orange. Would it be possible that the male Colour Sergeant occurs in two "forms" - one with the white subapical spot, and the other with an orange subapical spot? Or is the difference in the colour of this spot too insignificant for the male to be considered dimorphic?

2) The female Blue Pansy (Junonia orithya wallacei)

A typical female Blue Pansy with all-brown hindwings

This common urban species is widely distributed in Singapore, primarily due to the abundance of its caterpillar host plant, the Chinese Violet (Asystasia gangetica). The male is distinctive, with its attractive bright blue hindwing and cannot be confused with any other species in the region. The female, which is described as coloured with more sombre hues, and has a half bluish-grey hindwing.

A female Blue Pansy with extensive blue shading on the hindwing

A female Blue Pansy with a moderate blue shading on the hindwing

A female Blue Pansy with almost all-brown hindwing, and only slight blue shading at the dorsum of the hindwing

The colour of the hindwing of the female ranges from the post-discal half of the hindwing blue to totally brown with no hint of blue at all. Whilst the diagnostic pair of large orange-red post-discal ocelli on the hindwing is always consistent, it is the colour of the hindwing that may offer some interest to researchers to dwell further on the subject of whether the female Blue Pansy could be dimorphic.

A pair of Blue Pansy (left : male and right : female).  The female has all-brown hindwings

An all-brown hindwinged female Blue Pansy

A female Blue Pansy with strong blue shading on the hindwing

Whilst the extent of the blue colour on the hindwing of the female Blue Pansy is variable, the occurrence of totally brown females with no blue presents a question of whether there could be genetic variation at work that could point to some form of dimorphism in the females. As there are no distinct seasonality of the occurrence of the blue and brown hindwinged females, it is unlikely to be a subject of dry or wet season forms here.

3) The Common Tit (Hypolycaena erylus teatus)

A Common Tit displaying the typical pale greenish grey underside with slight ochreous brown termen and orange post-discal bands on the underside of the wings

This small and common urban species can be found in Singapore's parks and gardens as well as on the fringes of the forested nature reserves. In this species, the range of the colour of the underside of the forewing ranges from pale greenish grey with "weakly shaded with ochreous brown along the termen" to a very strong and obvious orange shading appearing like a submarginal band on the forewing.

Another typical "grey form" of the Common Tit with slight orange shading along the termen of the forewing underside

An "orange form" of the Common Tit with extensive orange shading on the underside of the forewing, making it appear like a band along the termen margin

A Common Tit with extensive orange shading across both wings

In some pristine individuals, the orange underside is so distinct as to even closely resemble the related species, the Dark Tit (Hypolycaena thecloides thecloides) whose underside of the wings are consistently orange. At the other end of the spectrum, there are individuals of the Common Tit that appear almost grey, with the post-discal bands a deeper orange-brown compared to the brighter orange bands in the orange "form".

Another Common Tit with strong orange shading along the termen of the forewing

A Common Tit with slight orange shading at the termen of the forewing

A Common Tit with minimal orange shading along the termen, making it appear grey compared to the extensive orange "form"

Would the variations in the colour of the underside of this species suggest some form of dimorphism? Individuals of the orange or grey "forms" appear consistently enough to imply that these are not aberrations. Is there a possibility of two different forms of the Common Tit? This is a subject that may be worth pursuing by researchers who are keen to take this observation further.

The observations here are for discussion, and certainly does not claim to be conclusive with any scientific rigour. The possibilities of dimorphism of these species with distinct forms will have to be researched and studied further.  But the observations are intended to spark off further thoughts and considerations for those who may be interested to find out more.

Text by Khew SK : Photos by Foo JL, Khew SK, Lim CA, Loh MY, Michael Soh, Horace Tan and Anthony Wong