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

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.

300 !!!

300 !!! - Discovery of the Yellow Streak Darter
Species #300 on the Singapore Checklist

And so, after many years, Singapore's Butterfly Checklist has passed the 300 mark once again. The early authors had recorded at least up to 361 species (Ref : Butterflies of the Malay Peninsula and Butterflies of West Malaysia and Singapore), but many have gone extinct or have not been reliabily seen in the past two decades. At the same time, many new species not recorded by the early authors have also be documented and added to the checklist.

It was a memorable outing for ButterflyCircle members on 26 Feb 2011. It was on this day that BC members re-discovered the Wanderer. Amidst the excitement of finally seeing that elusive species in Singapore, there was another less attractive butterfly that was shot by BC member Simon Sng. Coincidentally, this outing was organised by Simon and it is a well-deserved 'prize' that Simon bagged with the shot of this skipper which will be recorded as Singapore's 300th species.

Simon's shot is the first one taken of this species in Singapore

Although Simon's record shot was not of his usual standard of photography, it was sharp enough to show that this species was not anything that has been seen in Singapore before. The deep yellow undersides marked with rather distinctive markings revealed that this was a species that is new to Singapore.

A bit of artistic licence to dramatise the celebration of the 300th species in Singapore! Image copyright © Warner Bros

With this species, we have reached the 300 mark - a long way from the time when veteran Steven Neo started recording a checklist for Singapore in the early 90's. Species that Steven documented, like the Red Base Jezebel, Common Pierrot and Pointed Palmfly, to name a few, have yet to be seen again in Singapore since the days he was active in maintaining the Singapore Checklist.

Another shot of the Yellow Streak Darter taken by Simon on 26 Feb 2011

Steven and I co-wrote a paper in the Gardens' Bulletin Singapore, a refereed journal by the National Parks Board in 1997. The paper, entitled "Butterfly Biodiversity in Singapore with Particular Reference to the Central Catchment Nature Reserve" was published in Issue 49 (1997) of the Gardens Bulletin. The paper appears on pages 273-296 of the publication. Back then, armed with film SLRs and a net, we managed to record only 236 butterfly species in Singapore.

With the growth of ButterflyCircle's membership in the 2000's and especially after 2005, and over the past 5-6 years, we have added a total of 64 additional species to the Singapore Checklist. With more eyes (and sharp lenses) over the years, and hardworking members of ButterflyCircle have added a number of rare species to the Checklist. When ButterflyCircle launched its Field Guide to the Butterflies of Singapore in Oct 2010, we had reached a total of 296 species.

Coming back to our little "Spartan" species #300, - Long-time butterfly photographer, Simon knew at once that he had shot something different, though the butterfly sped off after he shot it. When Simon showed me the skipper, I was also stumped as I'd never seen this species before in my years of collecting and studying butterflies.

At BC's forums, other experts joined in and we narrowed it to a Salanoemia sp. with the closest recorded species being Salanoemia similis in Malaysia. Determined to nail down the ID of this mystery species, I went to the same location on Pulau Ubin the next day, and after about 3 hours of searching, the yellow skipper zipped right in front of me. With better shots of the skipper, we concluded that the skipper is a Yellow Streak Darter (Salanoemia tavoyana), as the distinctive markings of this individual puts the ID well beyond doubt, after cross-referencing to various books and internet resources.

What is surprising is that C&P4 states that this species is found in Kedawi (Kedah and Langkawi in the north of the Malay Peninsula) and Myanmar. How it appeared so far south of its normal geographical distribution is beyond our comprehension. We found a caterpillar near the location where this individual was shot, so we hope that we may have discovered the early stages of this species as well.

The pristine individual observed suggests that it may have eclosed recently, and is definitely not the condition that a butterfly would be in, if it had migrated to Singapore after a long flight. So will we see more of this species in future? It's anybody's guess. But in future, we will surely take a second look at any yellow skipper that flies in our paths.

So Singapore welcomes its 300th species on 26 Feb 2011. There will certainly be more to come, and we have already confirmed the existence of species #301! Watch this space!

Text by Khew SK ; Photos by Khew SK & Simon Sng

References :

• [C&P4] The Butterflies of The Malay Peninsula, A.S. Corbet and H.M. Pendlebury, 4th Edition, Malaysian Nature Society.
• Butterflies of West Malaysia & Singapore, W.A. Fleming, 2nd Edition, Longmans
• Butterflies of Thailand, Pisuth Ek-Amnuay, 1st Edition, 2006

Acknowledgements :

• Special thanks to Dr Laurence Kirton of FRIM for his comments on the ID of this species.