Butterfly of the Month - April 2025

Butterfly of the Month - April 2025

The Yellow Streak Darter (Salanoemia tavoyana)

A Yellow Streak Darter resting on a frond of a fern

We have passed the first quarter of the year and the world has become a lot more volatile and chaotic as we move into the 2nd quarter. Over in the USA and the rest of the world, 'tariff' has become the most searched-for word on the internet. After the US President rolled out his Liberation Day measures, the economic world suffered a nasty shock as billions were wiped off the stock markets around the world. And as if riding a roller coaster, the markets reacted violently to policy reversals - up and down, in just a matter of days.

A Yellow Streak Darter sipping nectar from the flower of the Singapore Daisy

And it's not something that is going to be over quickly as a new normal will begin to change how the world moves on from this. The trade war's victims will probably be the average man-in-the-street who will have to struggle with an even higher cost of living to cover daily essentials and necessities. It is amazing how global equilibrium can be disrupted so easily by one man and in so short a time without resorting to any violence or hostilities... yet.

Over in Singapore, election fever has gripped the population, as Nomination Day and Polling Day have been confirmed for 23 April and 3 May respectively. In an already chaotic world, how will the incumbent political party fare with the citizenry? Will the ruling party wrest back constituencies that it lost in the previous election? Or will it lose even more ground to an already strengthening opposition presence? The electorate will decide in a couple of weeks' time.

April 2025 is an unusually wet month for the region, with storm surges causing flash floods in Malaysia and Singapore. Commensurately, butterfly activity has also been lacklustre and low. The wet and cooler weather seems to have put a dampener on the numbers of butterflies out and about in our favourite butterfly hunting locations all around the island.

A Yellow Streak Darter perched on a leaf of its caterpillar host plant, the Mangrove Fan Palm

This month, we feature yet another "exotic" or non-native species that was a new discovery for Singapore when it was first observed and recorded in Feb 2011 on the offshore island of Pulau Ubin - the Yellow Streak Darter (Salanoemia tavoyana). First observed at a heavily shaded area near the Sensory Trail on Pulau Ubin, it has since been spotted elsewhere on Ubin at other locations where the caterpillar host plant, Licuala spinosa (Mangrove Fan Palm) grows. The host plant is not rare and is found on Singapore island where it is often used as a landscaping plant in many parks, gardens and roadside greenery.

The first field shot of this species taken in Singapore in Feb 2011

The species was described as "known only from South Burma, Kedah and Langkawi", so it's a mystery as to how it appeared in Singapore! After its discovery, it has continued to be regularly seen on Pulau Ubin, although observations of its caterpillars far outnumber observations of the adult butterflies.  The unique eating pattern of the caterpillars and the construction of leaf shelters make them easy to spot on the Mangrove Fan Palm that grows all around the island.

A Yellow Streak Darter shot in its typical environment in deep shaded forested habitat

The upperside of the Yellow Streak Darter is brown with a series of hyaline yellow spots and streaks.  There is a prominent yellow streak on the basal half of the forewing. There are two yellow cell spots which are the diagnostic feature of this species. The antennae are yellow just below the apiculus with the shaft banded with yellow and brown. The eyes are a solid dark brown and large.

The underside is a rich yellow with dark spots and a characteristically obviously yellow-centred cell spot. The marginal areas of both wings are a deeper orange-yellow.  The abdomen is chequered with yellow and brown with the legs a solid orange-yellow and unmarked. The wingspan of the adult ranges from 29-32mm.

Yellow Palm Dart adults are usually observed perched on the uppersides of foliage in heavily shaded forested areas where they frequent. When disturbed, they fly off rapidly in the usual Skipper-like fashion. This species' field behaviour is reminiscent of related species like the Yellow Chequered Lancer and Chequered Lancer. The complete life history has been recorded on this blog here.

Text by Khew SK : Photos by Khew SK, Koh CH, Richard Ong, Michael Soh, Simon Sng, Horace Tan and Zick Soh.

Further Reading : 

• Life History of the Yellow Streak Darter

Interesting Ubin Butterflies

Interesting Ubin Butterflies
Featuring 10 Butterflies on Pulau Ubin

Our first weekend blogpost for 2019 showcases 10 species of butterflies that are more often spotted on Pulau Ubin than any other location in Singapore. Some are not uncommon when they make a seasonal appearance, whilst others are rare and seen only once or twice on the island. Quite a few of the species featured in this article include newly discovered/re-discovered species for Singapore.

The male Malayan Birdwing (left) was spotted on Pulau Ubin, whilst the female was bred from a caterpillar found at Alexandra Hospital Butterfly Trail

Amongst the Papilionidae, two species are noteworthy. The first is the Malayan Birdwing (Troides amphrysus ruficollis). A re-discovered species that was first documented in 2011, a free-ranging male was photographed in late Nov 2013 on Pulau Ubin. Recorded as extant in the early authors' checklists, the Malayan Birdwing has not been seen in Singapore for a long time. The species is known for its wide flight range and the male spotted in Nov 2013 could have been aided by the North-easterly winds during the monsoon months of the year in this region.

A Common Jay feeding on the flower of the Buas-Buas bush at Pulau Ubin

A puddling Common Jay shot at Pulau Ubin in 2004

The second Papilionidae is the Common Jay (Graphium doson evemonides). A new discovery when it was first spotted in 2004, the species is regularly seen on Pulau Ubin. Given that its caterpillars can feed on a number of relatively common host plants on the island, the colony of Common Jay that currently still exists on the island is probably quite sustainable. Even as recent as in Jan 2019, a Common Jay was spotted feeding on the flowers of Lantana at Butterfly Hill.

A recent addition to the Singapore Checklist in 2018, the Orange Gull was spotted puddling at Pulau Ubin

A recent re-discovery amongst the Pieridae, is the Orange Gull (Cepora iudith malaya), that was spotted puddling on the island. Listed on the checklists of the early authors, this species has not been seen in the past three decades at least, until Dec 2018. Again, the theory that some of these strong-flying species were aided by the tail-winds of the North east prevailing winds could be true.

This female Wanderer was found near the Sensory Trail in 2011

Back in March 2011, a female Wanderer (Pareronia valeria lutescens) was photographed on Pulau Ubin. Although reports of the fast-flying males were made some time earlier, no reliable evidence of this species was available until this female was spotted perched on a leaf in the shady undergrowth. Again, considering the month that this species was found in Singapore, there could be a correlation with the North-easterly winds that are prevailing from around Dec to early March annually as defined by the Meteorological Services of Singapore website.

The Grey Glassy Tiger was observed at Butterfly Hill at Pulau Ubin

Amongst the Danainae, the Grey Glassy Tiger (Ideopsis juventa sitah) was discovered in Oct 2014. The robust Danainae, known for their toughness and migratory characteristics, are able to fly long distances and perhaps this individual made it to Pulau Ubin from up north. However, what is curious is that another individual was photographed at the Singapore Botanic Gardens in Jul/Aug 2015 that debunks any theory that these are wind-aided individuals that reached Singapore.

The Dwarf Crow is common and is regularly seen at Butterfly Hill on Pulau Ubin

The Dwarf Crow (Euploea tulliolus ledereri), first spotted on Pulau Ubin in 2002, continues to be regularly seen on the island and makes seasonal appearances where it can be considered common. Then it disappears altogether for several months and then re-appears again where up to five or six individuals can be observed together at nectaring plants on the island. Recorded as a re-discovery, the colony of Dwarf Crow is probably a sustainable population as it has been seen almost annually on the island.

The very rare Mangrove Tree Nymph made an appearance at Butterfly Hill at Pulau Ubin in 2013

One of our largest butterflies in terms of wing surface area, is the Mangrove Tree Nymph (Idea leuconoe chersonesia). This subspecies, which is mainly found in mangrove swamps in Malaysia, Singapore and Indonesia, is very rare and local. First observed during a survey of the butterfly fauna of Pulau Tekong, a Mangrove Tree Nymph was photographed on Butterfly Hill at Pulau Ubin in Jul 2013.

Spotted a number of times at Pulau Ubin, the Malayan Nawab was a re-discovered species for Singapore

The Malayan Nawab (Polyura moori moori) another re-discovery, has been spotted at least half a dozen times on Pulau Ubin. Given its similarity to the Plain Nawab (Polyura hebe plautus), it is likely that this species may have been missed earlier or misidentified as its commoner cousin. As recent as in Oct 2018, another individual was photographed again on Pulau Ubin. Thus far, the species has not been reliably seen on the main island of Singapore yet.

The White Banded Flat is a species regularly seen on Pulau Ubin but not elsewhere in Singapore

Amongst the Hesperiidae, another Ubin "resident" species is the White Banded Flat (Celaenorrhinus asmara asmara) which was first spotted in 2011. Unlike the vagrants or seasonal migrants, this species is extant on Pulau Ubin and a viable colony has existed till now. As recently as Jan 2019, the White Banded Flat has been spotted on the island.

The very rare Yellow Streak Darter was first discovered on Pulau Ubin in 2011.  Thus far, it has not been seen anywhere else in Singapore

The final species of the top 10 interesting Ubin butterflies is the Yellow Streak Darter (Salanoemia tavoyana). First discovered in 2011, this very rare species occurs on the island in a small localised colony. The caterpillars were found on the Mangrove Fan Palm (Licuala spinosa) and successfully bred to adulthood. However, the adult is rarely seen and prefers to lurk in heavily shaded vegetation.

There are likely to be several more species to be added to the Ubin list of unique and interesting butterflies, but that will be for another time.  Ubin is probably a convenient 'pit-stop' for migratory or stray butterflies coming from Malaysia, and more should be looked out for in future. 

Text by Khew SK : Photos by Bob Cheong, Federick Ho, Mei Hwang, Khew SK, Loh MY, Loke PF, Michael Soh, Horace Tan and Yong WH

Life History of the Yellow Streak Darter

Life History of the Yellow Streak Darter (Salanoemia tavoyana)



Butterfly Biodata:
Genus: Salanoemia Eliot, 1978
Species: tavoyana Evans, 1926
Wingspan of Adult Butterfly: 29-32mm
Caterpillar Host Plants: Licuala spinosa (Arecaceae, common name: Mangrove Fan Palm).


A Yellow Streak Darter taking nectar.


A Yellow Streak Darter sighted on a leaf perch.

Physical Description of Adult Butterfly:

Above, both sexes are dark brown with the forewing having a number of hyaline spots: two small sub-apical spots at the base of spaces 6 and 7, two large spots at the base of spaces 2 and 3, and two sub-equal spots in the cell. There is a yellow streak in the basal half or two-thirds on the forewing. Both sexes have a yellow discal patch on the hindwing and a yellow-colored costal margin, both of which are broader and more prominent in the male than in the female. In addition, the male has a sub-costal yellow streak in the basal half of the forewing, and a yellow-colored dorsal margin on the hindwing. Underneath, the wings are yellowish orange in base color with a number of irregularly-shaped post-discal black spots on both fore- and hindwings. Additional black spots are found in the cell and the base of spaces 1b, and 7 in the hindwing. Several of these spots take on the appearance of a yellow oval spots encircled in black. The blacks spots in the female are somewhat larger and more prominent than in the male.


The first sighting of a Yellow Streak Darter.

Another Yellow Streak Darter on a leaf perch.

Field Observations of Butterfly Behaviour:

This species was only recently discovered and added to the Singapore checklist as species #300. According to C&P4, the Malayan species of the genus Salanoemia are all very rare, and the Yellow Streak Darter is no exception. In Singapore, adult sightings have so far been very rare and only confined to the offshore island, Pulau Ubin.

A male Yellow Streak Darter.


A female Yellow Streak Darter.

Early Stages:


Host plant: Licuala spinosa.

The host plant, Licuala spinosa, is a palm with fan-like leaf in a pinwheel layout. The petiole is armed with spines. This plant can be found growing in back mangrove habitats or in gardens/parks as an ornamental and landscaping plant. The caterpillars of the Yellow Streak Darter feed on leaves of this plant, and live in shelters made by joining edges of leaf fragments together with silk threads.

A leaf shelter of a final instar caterpillar of the Yellow Streak Darter.

The eggs are laid singly on the leaf of the host plant. Each hemispherical egg has four concentric colored zones, starting from the centre and moving outwards, the colors are dark pinky red, reddish brown, pinky white and finally dark pink red. The micropylar sits atop. There are 20 disheveled radial ridges in all. The base diameter is about 1.4mm.


Two views of an egg of the Yellow Streak Darter.


A mature egg with the young caterpillar already nibbled away the polar part of the egg shell.

It takes about 4 days for the collected egg to hatch. The young caterpillar eats just enough of the shell to emerge, and has a length of about 3mm. Its has a cylindrical body shape, very short dorso-lateral and sub-spiracular setae and a tuff of long setae at the posterior end. The body is mainly orange in base color with faint reddish bands running dorso-laterally. The head capsule is yellowish brown.

A newly hatched 1st instar caterpillar with its empty egg shell nearby.


Two views of a newly hatched caterpillar, length: 3mm.

The body color changes to pale yellowish green after a few feeding sessions on the leaf. The newly hatched constructs its leaf shelter as one of its first tasks after the hatching. Between feedings, the caterpillar retreats to its shelter for rest and security. By the time the caterpillar lies dormant in its shelter for the moult to the 2nd instar, its length has reached about 5mm. The 1st instar takes about 2-3 days to complete.

1st instar caterpillar, late in this stage, dormant prior to its moult, length: 5mm.

The 2nd instar caterpillar is whitish, but appears to be yellowish green with its "stomach" contents showing through the translucent cuticle. The short dorso-lateral and lateral setae are now absent. The anal plate still carries a few setae but these are not as long and prominent as in the 1st instar. The head is pale yellowish brown. This instar lasts about 3-4 days with the body length reaching about 8mm.

Two views of a 2nd instar caterpillar, early in this stage, length: 4.5mm.


A 2nd instar caterpillar hard at work at carving out a leaf fragment. The fragment (with a small portion not cut) will be joined to the uncut portion to form its shelter.


Two views of a 2nd instar caterpillar, late in this stage, length: 7.5mm.

The 3nd instar caterpillar resembles the 2nd instar caterpillar closely in body markings and coloration. This instar lasts about 5-7 days with the body length reaching about 11mm.

Two views of a 3rd instar caterpillar, female, early in this stage, length: 6.8mm.


Two views of a 3nd instar caterpillar, later in this stage. length: 9.5mm.

The 4th instar caterpillar is pale yellowish white in body color with a light green undertone. The head capsule is pale beige brown with two lateral white stripes sitting just above the mouth parts. Dark brown meshed markings adorn the surface above the white stripes. This penultimate instar lasts 5-7 days with the body length reaching up to about 18mm.

Two views of a 4th instar caterpillar, female, length: 17mm.


A 4th instar caterpillar, male, late in this stage, length: 19mm.

The 5th (and final) instar caterpillar closely resembles the 4th instar caterpillar with few variations. The head capsule has a base color ranging from pale beige brown to greyish white, and it appears to have more extensive black meshed markings than in the previous instar. This instar takes about 9-10 days to complete with the body length reaching up to about 26mm. On the last one to two days of this instar, the still feeding caterpillar secretes a thin layer of whitish substance on the lower sides of its body.

A newly moulted 5th instar caterpillar.


Two views of a 5th instar caterpillar, length: 24mm.


A 5th instar caterpillar, male, late in this intar, length: 26mm.


A 5th instar caterpillar in the field. Hard at work in repairing its damaged leaf shelter.

Towards the end of the 5th instar, the the body of the caterpillar shortens and its coloration changes to a translucent pale green. Soon it becomes dormant in its leaf shelter and enters the prepupatory phase which lasts for one day During this time period a copious amount of white waxy substance is deposited within the tight confine of the leaf shelter.

A pre-pupa of the Yellow Streak Darter.

Pupation takes place within the leaf shelter. The pupa does not secure itself with any cremastral attachment nor any silk girdle. It is pale brown in the anterior end, pale greenish in the rear thorax and wing cases, and pale yellowish brown in the abdomen. Length of pupae: 14.5-17.5mm.


Two views of a pupa of the Yellow Streak Darter.

On the last day of the pupal period, the pupa becomes mostly brown to dark brown. Yellow markings against a dark brown background are now visible in the wing cases. Finally after about 8 days of pupal phase, eclosion takes place with the adult emerging from the pupal case.


Two views of a mature pupa of the Yellow Streak Darter.


A newly eclosed male Yellow Streak Darter.


A newly eclosed female Yellow Streak Darter.

References:

• [C&P4] The Butterflies of The Malay Peninsula, A.S. Corbet and H.M. Pendlebury, 4th Edition, Malayan Nature Society.
• Butterflies of Thailand, Pisuth Ek-Amnuay, 1st Edition, 2006

Text by Horace Tan, Photos by Simon Sng, Khew SK and Horace Tan.