The Grass Yellows of Singapore (Part 1)

The Grass Yellows of Singapore (Part 1)

This blog article features the genus Eurema which comprise comparatively small, deep-lemon yellow butterflies with black borders. The Eurema, often referred to as the "Grass Yellows" are relatively common in Singapore, although there are actually six distinct species occuring on the island, and one of the species is a recent re-discovery and its habitat is threatened with development.

The more common species are found throughout the island, from urban areas to the forested nature reserves. At times, they can be abundant, where hundreds can be seen fluttering in an almost 'migratory' fashion in certain parts of the island. However, these rare 'break-outs' are seasonal, and could have been triggered by a variety of factors - from abundance of host plants, to the absence of predators and parasitic insects which keep the population in check and maintains a balance in nature.

The Grass Yellows are generally weak flyers, fluttering low around bushes and flowers. The caterpillars of the species feed on Leguminosae and it is known that various species have various alternative host plants. Amongst the favourite genera are Cassia (Senna), Caesalpinia, Paraserianthes (Albizia), Acacia and many others.

The identification of the species of Eurema is often not easy, particularly when the butterflies have a rather restless flight, and are alert when approached. The main identifying characteristics rely on certain distinguishing markings, particularly the number of spots at the cell on the underside of the forewing. The following is an identification key to the separation of the species in the genus :

Eurema species with no cell spots on the underside of the forewings

Eurema brigitta senna (No Brand Grass Yellow) - Upperside forewing black apical border serrated but not more deeply excavated in spaces 2 & 3. Male has no brand.

Eurema species with one cell spot on the underside of the forewings

Eurema sari sodalis (Chocolate Grass Yellow) - Underside forewing apical area entirely dark brown.

Eurema andersonii andersonii (Anderson's Grass Yellow) - Underside forewing apical area not entirely darkened. Inner edge of black border in space 1a and 1b inclined slightly towards tornus. Upperside black distal border not more deeply excavated in space 2 than in space 3.

Eurema species with two cell spots on the underside of the forewings

Eurema hecabe contubernalis (Common Grass Yellow) - Upperside forewing black border in space 1a and 1b at right angles to dorsum or sloping towards base.

Eurema simulatrix tecmessa - Underside forewing has a large cleft reddish brown apical spot.

Eurema species with three cell spots on the underside of the forewings

Eurema blanda snelleni (Three Spot Grass Yellow) - Upperside of the male with reduced and narrower black borders.

In Part 1 of this article, we feature three of the six Eurema species extant in Singapore.


The No Brand Grass Yellow (Eurema brigitta senna)



This species is a recent re-discovery, after missing from the Singapore checklist for a number of years. In an earlier blog article, we featured this species in detail. The No Brand Grass Yellow is the only species where the underside forewings are without cell spots. Upperside forewing black apical border serrated, but not more deeply excavated in spaces 2 and 3. Females are slightly more unique in that the yellow colour of the hindwings are lighter than the forewings on the undersides. The males' undersides are unicolourous as with the other species of this genus.

Both sexes undersides are covered with small brown 'freckles' which give the wings a rather spotted appearance, as compared to the other species in the genus. In certain individuals, the freckles are distinctly pronounced as to give the butterfly a very uniquely heavily spotted appearance, almost obscuring the clean yellow background colour of the wings.

The host plant of the species, Cassia mimosoides has been cultivated and located to other parts of the island in the hope of allowing the species to be translocated from its current habitat, which is under the threat of development. The species is highly vulnerable, although it can be common where its host plant occurs, and its preferred habitat of open sunny wasteland.

The Chocolate Grass Yellow (Eurema sari sodalis)

The Chocolate Grass Yellow is amongst the easiest of the genus to identify, especially when the butterfly stops to feed or puddle. The species' distinct solid brown apex on the forewing beneath sets it apart from the other species amongst the Eurema. The species is locally common, in locations where its preferred host plant is available.

However, it is not as widespread as the more common species of the genus, preferring the sanctuary of the fringes of the nature reserves in forested areas. It is more often encountered in well-vegetated areas of the forested parts of Singapore than flying in urban parks and gardens.

Where it occurs, males of the Chocolate Grass Yellows are often observed to puddle at sandy banks which have been tainted with fermenting organic matter, carrion and the like. Once it settles down to puddle, it remains quite still as it feeds, and allows an observer to get quite close to it.

The Anderson's Grass Yellow (Eurema andersonii andersonii)

This is a species that almost exclusively remains in the forested areas of Singapore's nature reserves. It is probably one of the rarer species of the genus (though one can argue that none of the species can be considered 'rare'). Usually seen singly, the Anderson's Grass Yellow features only one cell spot on the forewing beneath, like the Chocolate Grass Yellow. However, it does not have the former's solid brown apical patch.

Like its close cousin, the species has also often been observed to puddle at forest paths and sand banks of streams. In the morning hours, it also visits various flowering bushes as it feeds. Favourites are the white flowers of the Common Asystasia (Asystasia gangetica), the purple flowers of the Common Snakeweed (Stachytarpheta indicus) and several other wildflowers found in the forests.

The wings of the species also appear to be more rounded than its close cousins, and it has a comparatively more robust flight. At times it tends to have a habit of fluttering around low bushes, and then settling on the undersides of leaves.

Text by Khew SK ; Photos by Khew SK

References:

• The Butterflies of The Malay Peninsula, A.S. Corbet and H.M. Pendlebury, 4th Edition, Malayan Nature Society.

Life History of the Green Imperial

Life History of the Green Imperial (Manto hypoleuca terana)



Butterfly Biodata:
Genus: Manto de Nicéville, 1895
Species: hypoleuca Hewitson, 1865
Subspecies: terana Seitz, 1926
Wingspan of Adult Butterfly: 36mm
Caterpillar Host Plants: Macrosolen cochinchinensis (Loranthaceae)

Physical Description of Adult Butterfly:
Above, the male is shining bluish green, with the apical two-thirds of the forewing, cell and termen border of the hindwing black; tornal margin white and crossed by submarginal spots. The female is dark brown and has white tornal area in the hindwing crossed by conjoined quadrate black spots in spaces 1b and 2. Beneath, both sexes are yellowish orange on the forewing, much paler at dorsum and darker towards the apex. The extent of the yellowish orange coloration on the hindwing differs in the two sexes, with the male having almost complete coverage and that of the female being restricted to the costal area and white elsewhere. The white tornal area contains prominent subtornal markings, with a series of post-discal striae usually reaching vein 6. Each hindwing has a pair of white-tipped tails at ends of veins 1b and 2, with the ones at vein 1b much longer, and the ones at vein 2 about one-third as long.



A male Green Imperial


The upperside of a male Green Imperial


A female Green Imperial


The upperside of a female Green Imperial

Field Observations of Butterfly Behaviour:
This species was confirmed to be still extant in Singapore after a fortunate encounter with a male specimen at the edge of the nature reserve in 2008. It is rare locally as well as in the Malayan Peninsula. Sightings of this species have so far been confined to a few locations within the Central Catchment Nature Reserve, and typically only a single individual appears each time. The fast-flying adults have been sighted taking nectar at flowering plants in the reserves, and perching high near its host plants. An active ButterflyCircle member, Ben Jin, had the good fortune of locating the eggs and caterpillars on the host plant recently. Credit is thus due to him for the discovery of early stages of this stealthy species and making it possible for the life history to be featured in this article.

Early Stages:
The host plant, Macrosolen cochinchinensis, is a parasitic shrub with all parts of the plants glabrous (having no hairs, smooth). The leaves are leathery, opposite, ovate or lanceolate. The early stages of the Green Imperial feed on the young to mid-aged leaves of this parasitic host, with the 1st instar initially skimming the leaf surface and the later instars eating the leaf along the edges.


Host plant : Macroseolen cochinchinensis

Eggs are laid singly on the stem or petiole of a young shoot, or the pedicel in the vicinity of the flower buds of the host plant. The egg is hemi-spherical with a raised dome, the very top of which is the micropylar. Each egg is white and covered with rather large hexagonal pits. The diameter of the circular base is about 1mm.


Two views of an egg of the Green Imperial


Two vlews of an empty egg shell where the raised dome was mostly eaten by the newly
hatched as it made its way out.

It takes about 3 days for the collected egg to hatch. The young caterpillar consumes just enough of the egg shell to emerge. It is pale yellow in coloration, and has a length of about 1.5mm. Long setae (hairs) run along the length of the body dorsally as well as sub-spiracularly. Raised dorsal tubercles are transparent. A large prothoracic shield, in darker shade of brown, can be observed. The newly hatched feeds on the flower parts or the young leaves nearby by skimming the surface. Later instars will feed on the leaf lamina, working their ways along the edges.


Two views of a newly hatched caterpillar, length: 1.5mm.


1st instar caterpillar, length: 2mm.

As it grows in this instar, the caterpillar assumes a greenish (yellowish green form) or a reddish coloration (red form). The 1st instar lasts about 3 days and sees the body length increased to about 3mm.


A 1st instar caterpillar of the yellowish green form, in the vicinity of an egg.


A 1st instar caterpillar of the red form.

In the 2nd instar caterpillar, the dorsal tubercles are reduced in size, and the long dorsal setae seen in the 1st instar are now absent. Its diamond-shaped prothoracic shield is very dark in color. The posterior segments from the 7th abdominal segment onwards are fused together and taper downward to the last segment. Pale brown patches decorates the sides of the body, as well as the anterior and posterior segments.


A newly moulted 2nd instar caterpillar (yellowish green form), eating its old skin.


A red form caterpillar seen just after its moult to 2nd instar.


Two views of 2nd instar caterpillar (yellowish green form), early in this stage, length:4.5mm.

These patches become darker in coloration as the caterpillar grows in this instar. A much darker marking is also present between abdominal segments 4 and 5. It is possible to observe the dorsal nectary organ at this stage, though it is still inconspicuous to the naked eye. The 2nd instar lasts for 3 days with the body length reaches about 6-7mm.


Two views of a 2nd instar caterpillar, later in this stage, length:6mm.



A 2nd instar caterpillar committing a carnivorous act.
The victim is a young caterpillar (late 2nd instar) of Tajuria mantra mantra.

In the 3rd instar caterpillar, the lateral body markings, pale brown to dark brown in cryptic pattern, now dominate the general appearance. In the red form, these lateral body markings have a reddish undertone. The lateral body markings are broken between the 4th and 5th abdominal segments by a black triangular marking. The contrasting green coloration is restricted to the dorsal ridge and subspiracular rim of the body.


3rd instar caterpillar, length: 9.5mm.

As the body grows in size to a length of around 11-12mm, the color of shading on the body darkens. The dorsal nectary organ and the tentacular organs are now easily observed on the fused posterior segments. After 3-4 days in the 3rd instar, the moult to the 4th and final instar takes place.



3rd instar caterpillar, length: 12mm, resting for the moult to next instar.

The 4th instar caterpillar is dark brown in color, with pale brown lateral patches and very wrinkled body surface. Both yellowish green and red forms now have the same appearance in this final instar. The prothoracic shield is initially purplish in color in the early hours of the moult, but turning black soon after.


Three shots of the moutling event from the 3rd to the 4th instar,
ending with the new 4th instar eating its old skin.



Prothoracc shield of the 4th instar caterpilar, initially purple (top) and turning black hours later (bottom)

4th instar caterpillar, length: 12.5mm

The 4th instar lasts for 4-6 days and the body reaches a length of about 21-23mm. Nearing the end of this instar, the caterpillar ceases feeding, and its body shrinks in length. Soon it comes to rest on a spot on the surface of a leaf or a stem, and begins the pre-pupatory phase of its life cycle.


4th instar caterpillar, late in this stage, 21mm

A sequence of shots showing the eversion of the tentacular organs.

The pre-pupatory caterpillar prepares for pupation by spinning a silk pad to which it attaches itself via claspers at the posterior end. Even during this pre-pupal stage, color changes continue to take place with silver replacing the pale brown coloration during the 1.5-2 days of the pre-pupatory period.

A pupation sequence for a Green Imperial caterpillar.

Finally after 16-18 days of larval growth, pupation takes place. The pupa is held firmly via its cremaster to the silk pad on the stem or leaf surface. It is 15-16mm in length, brown to reddish brown in base color with large pale green patches. The pupa was observed to react to an external disturbance by jerking up and down.


Two views of a fresh pupa of Green Imperial

Eleven days later, the pupa becomes darkened in color signaling the imminent emergence of the adult. The next day the adult butterfly emerges from the mature pupa.


Two views of a mature pupa (female)


A newly eclosed male Green Imperial drying its wings on its pupal case.


A newly eclosed male Green Imperial.


A female Green Imperial

References:

• 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 Mark Wong, Tan Ben Jin, Khew SK and Horace Tan

Butterfly of the Month - April 2009

Butterfly of the Month - April 2009

The Chequered Lancer (Plastingia naga)

This is the first time that we are featuring a species of the family Hesperiidae as our Butterfly of the Month. The Hesperiidae, or commonly referred to as Skippers, are fast-flying butterflies. An earlier blog article - The Speedsters of the Butterfly World - the Skippers, introduced this family of butterflies, which occupy a position between true butterflies, and true moths.

Skippers are generally drab coloured and not considered the most attractive of butterflies. However, they are significant in their number of species and due to their relatively understudied status, more species remain to be discovered.

The Chequered Lancer (Plastingia naga) is one of two species representing the genus Plastingia in South-east Asia. It is a small butterfly, usually not exceeding 35mm wingspan. The upperside is dark brown with whitish yellow hyaline spots and yellow-orange streaks at the wing bases. The hindwing bears a pale yellow inter-neural streaks. The underside markings are unique in featuring black veins with rectangular spots on a white background, giving the butterfly a chequered appearance.

The species is fast-flying, and is on the wing from early morning to noon, and prefers to rest in the shady forest understorey for most part of the rest of the day. When disturbed, the Chequered Lancer takes off at high speeds, but often comes back to a few favourite perches to rest with its wings folded upright.

The Chequered Lancer has an interesting scientific name, naga. In Southeast Asian folklore, naga refers to a serpentine creature that reportedly inhabits the Mekong River in Cambodia and Thailand. Revered as a Buddhist religious symbol, the Naga has a body like that of an anaconda and the head of a dragon, and legends say that it can spit great red balls of fire into the sky.

A Chequered Lancer strikes an unusual pose showing the markings on the forewings only

How this species came to be named after a serpent is curious, and would be an interesting subject for trivia research into the names of butterflies. Perhaps the black-and-white chequer-board appearance is reminescent of the scales of the dragon's body?

The species is moderately common in shady habitats where its preferred host plant, the Fishtail Palm (Caryota mitis) is found. It is found in urban parks as well as the forested areas of the nature reserves in Singapore. Usually found singly, individuals observed tended to fly around and stop on the top surfaces of leaves in the vicinity of its host plant. Photographing them can be quite challenging in the low light situations but occasionally, one will encounter a cooperative Chequered Lancer that will stay still for a few photogenic shots.

A Chequered Lancer perches on a leaf of its host plant. Note the extended palpi in this individual

Like many species of the Hesperiidae, the Chequered Lancer is sensitive to the camera's flash at times, and may 'jump' when the flash goes off. However, once it gets used to the flash, it will stay quite still for subsequent shots.

The caterpillar behaves like many of the Hesperiidae, forming leaf shelters within which it stays 'protected' and moves out to feed on other parts of the leaf. After reaching the final instar, the caterpillar also pupates in its leaf shelter.

A Chequered Lancer's 'baby photo' - a final instar caterpillar with its leaf shelter opened to expose the resident

Males and females are generally similar in appearance, though the females tend to be larger in size, darker and with fewer hyaline spots on the wings.

Text by Khew SK : Photos by James Chia, Chan SC, Tan BJ, Mark Wong & Khew SK