29 November 2020

The Disappearing Acts 2

The Disappearing Acts 2
Now You See Me, Now You Don't

A No-Brand (or Small) Grass Yellow (Eurema brigitta senna) feeding on the flower of the Coat Buttons (Tridax procumbens)

In an earlier blogpost about some butterfly species that have been documented as extant species historically, we featured some species that appeared over a period of time, when several pristine individuals were seen for several weeks. Then for some mysterious reason, they disappeared altogether and not seen for many years. They appeared in very localised areas in Singapore, and may even be temporarily common, but have not been seen since.

A Pitcher Blue (Virachola kessuma deliochus) perched on the fruit of the Singapore Rhododendron (Melastoma malabathricum)

In this weekend's blogpost, we take a look at three extant species that are relatively small in size, and unlikely to be migratory or stray species in the local environment. However, after appearing for a short period of time, two of these species have not been spotted for many years thereafter. Having been recorded by the early authors, these species were not reliably recorded for many decades, until the period between 2006 and 2009, when two of these species were observed in very localised areas in Singapore.

A White Fourline Blue (Nacaduba angusta kerriana) perched on a leaf in the forest understorey

Then they disappeared, and were not seen for many years since. It is not known where they disappeared to in the meantime. As they are not all forest-dependent species, where do they go to? Perhaps in some localised area where they have not been spotted yet? Or do they have some sort of hibernation mechanism in their life-history biology that allows them to delay eclosion for a long time?

A female No-Brand Grass Yellow ovipositing on its host plant. Cassia mimosoides

Interestingly, when they appeared in Singapore, all their life histories were recorded on their respective caterpillar host plants. Their life histories are documented here on this blog. From the records that are shown here, their early stages are quite normal and there is nothing out of the ordinary that suggests that they have special characteristics compared to other butterflies.

1. The No-Brand (or Small) Grass Yellow (Eurema brigitta senna)

A female No-Brand Grass Yellow feeding on the flower of the Coat Buttons

The No-Brand Grass Yellow (also called Small Grass Yellow) was a recorded as a re-discovery in 2006 when it was spotted at an open patch of land in Punggol that was cleared for future development. Its caterpillar host plant, Cassia mimosoides grew wild as a "weed" in the area. For a period of about up to a year or so, the species was quite common at that site, and mingled with many of the urban and scrubland butterfly species.

A female No-Brand Grass Yellow ovipositing on its host plant, Cassia mimosoides

Today, a new public residential project is under construction at the site, and the open wasteland with secondary forest growth is no longer there. With that, the No-Brand Grass Yellow has disappeared. Efforts were made to cultivate its host plant in various places, and the caterpillars and pupae translocated to the other sites, but to no avail. The species has not been seen for a long time since then.

Upperside of the No-Brand Grass Yellow showing the scalloped black borders
A male No-Brand Grass Yellow perched on a leaf.  Note the heavily-speckled wings

The species looks very similar to many of its other Eurema cousins that are common all over Singapore. The main different on the upperside is that the black borders are regularly scalloped, unlike the deeply excavated black borders of the other species. On the underside, there are no cell spots, and the wings are heavily peppered with brown freckles all over. The underside of the female is more distinctive in that the hindwing is a paler yellow than the forewing.

2. The White Fourline Blue (Nacaduba angusta kerriana)

A White Fourline Blue perched on a leaf

The next feature species is a small butterfly with a wingspan of only about 30-35mm.  The White Fourline Blue was again, recorded as a re-discovery in 2009 at Telok Blangah Hill Park. It was a surprise as the species was documented as an extant species in Singapore by the early authors, but was not seen until 2009 - and even so, at an urban park. Was it one of the remnant species that survived despite the urban development in Singapore?

A mating pair of White Fourline Blues

When it appeared, there were several individuals fluttering around the shaded shrubbery, and we even encountered a mating pair of the species, suggesting that there was a small, but critically-endangered colony in that location. Fortunately, our life histories expert, Horace Tan, spotted a female ovipositing on its host plant, Entada spiralis and managed to document its life history successfully.

Upperside of a newly-eclosed female White Fourline Blue

The male White Fourline Blue is purplish blue above with a thin black border. The female has a broad black border on the forewing, and a light blue to whitish ground colour with diffuse greyish markings on both wings. The female is so distinctive that it cannot be confused with any other species in the Nacaduba genus. The underside is greyish ground colour with broad white diffuse markings. There is a prominent black rounded submarginal spot in space 6 of the hindwing.

3. The Pitcher Blue (Virachola kessuma deliochus)

A Pitcher Blue perched on the flower of the Coat Buttons

Unlike the preceding two species, the Pitcher Blue is an extant rare species that was re-discovered in the early 1990's at a site near the nature reserves in Chestnut Forest. It was subsequently spotted at Kent Ridge Park and other areas in the Southern Ridges. It was only until it was again observed at Bukit Batok Forest that its life history was recorded.

The species depends solely on the caterpillar host plants from the Nepenthes genus - commonly called Pitcher Plants or Monkey Cups. These plants prefer hilltops and rather dry, rocky areas to grow. Today, these plants are not common (due to habitat destruction and poaching) and this has possibly affected the survival of the Pitcher Blue. That the caterpillars feed inside the seed pods of the Pitcher Plant makes it even harder to survive without the plant, and the fact that the plant has to flower and fruit as well!

Upperside of a female Pitcher Blue

The male is a deep shining blue above with a broad black apical border on the forewing. The female is a light greyish-blue with narrower borders. The underside is grey with the typical white striae, resembling the Nacaduba species. The hindwing has a filamentous white-tipped tail at vein 2 of the hindwing. The Pitcher Blue is still occasional sighted, particularly at flowering trees like the Syzygium but sightings are erratic and it may not be seen for several years before another one turns up again.

Where are these species of butterflies today? Are they still lurking around somewhere, undiscovered, in some patch of greenery in our parks and nature reserves? Why have they disappeared for years on end? When will they reappear again? Answers to these questions continue to elude us as we strive on to struggle to further our knowledge and understanding of our butterflies to help conserve them for future generations.

Text by Khew SK : Photos by Khew SK and Horace Tan

Life Histories :

22 November 2020

Favourite Nectaring Plants #18

Butterflies' Favourite Nectaring Plants #18
The Blood Flower (Asclepias curassavica)

An orange-hindwinged form-chrysippus Plain Tiger feeding on the flowers of the Blood Flower

Our 18th feature plant in the series of butterflies' favourite nectaring plants is a non-native "milkweed" that comes from tropical South America. This plant is better known locally in Singapore as one of two of the caterpillar host plants of the Plain Tiger (Danaus chrysippus chrysippus). The Blood Flower (or Scarlet Milkweed) is sometimes cultivated in butterfly gardens to attract and support the conservation of the Plain Tiger.

A white-hindwinged form-alcippoides Plain Tiger feeding on the flowers of the Blood Flower

The Blood Flower is a lactiferous plant from the dogbane family, Apocynaceae. When parts of the leaves or stems are snapped or damaged, a whitish milky fluid is excreted. This milky sap is poisonous and can cause skin irritation in sensitive people. The caterpillar of the Plain Tiger sequester the toxic constituents of the plant to make it distasteful to predators like birds. The adult butterfly is also distasteful, as are the other species in the Danainae sub-family, and displays aposematic colouration.

A lush patch of Blood Flower with healthy blooms
The Blood Flower is also known by several common names, one of which is "Scarlet Milkweed".  This is a sign at the Blood Flower patch at Gardens by the Bay

The plant is an evergreen erect herbaceous perennial, and grows up to 1.2m tall. It is usually cultivated for its attractive red and orange flowers.  There are also all-yellow flowered cultivars. The plant has a small spread and is never considered bushy. It is best cultivated in plant beds and as feature plants in landscaped gardens. For a better visual effect, 20 or more plants should be planted together.

Young Blood Flower plants grown together in a butterfly garden patch

The Blood Flower is considered a low shrub and sometimes cultivated in pots too. It flowers throughout the year and usually does best in open areas in full sunshine. It is an exotic and it does not grow naturally in Singapore and where it grows, it has usually been cultivated. Its region of origin is Tropical South America. Its presence in Singapore is limited to cultivated parks and gardens, usually grown as an accent shrub for its colourful flowers in combination with other flowering plants.

A Plain Tiger caterpillar munching on the flower of the Blood Flower

Plant Biodata:
Family: Apocynaceae
Genus : Asclepias
Species : curassavica
Synonyms : Asclepias bicolor, Asclepias margaritacea, Asclepias aurantiaca, Asclepias curassavica var. concolor, Asclepias cubensisAsclepias nivea var. curassavica
Country/Region of Origin : Central and Northern parts of South America, Mexico, Curacao
English Common Names : Blood Flower, Cancerillo, Sunset Flower, Pleurisy Root, Cotton Bush, Red-head, Indian Root, Swallow Wort, Scarlet Milkweed, Matal, Bastard Pecacuanha, Milkweed, Silkweed, Mexican Butterfly Weed
Other Local Names : Kakatundi, Madhar (Hindi),马利筋, 连生桂子花

Some butterflies love the attractive red and orange-yellow flowers of the Blood Flower

As a tropical plant, the Blood Flower blooms continuously throughout the year. It is relatively heat tolerant and and grows best in full sun with regular moisture. As the plant flowers and grows older, it is likely to look lanky and unattractive. It is then time to cut it down and let it sprout new shoots to regenerate growth again. The plant is susceptible to sucking insects like aphids and mealy bugs and is often attacked by these pests, particularly on the young shoots and growth of the plant, stunting its growth and turning the leaves yellow.

The green lanceolate leaves of the Blood Flower plant

The leaves of the Blood Flower are simple, opposite, shortly petioled, lanceolate to narrow-elliptic in shape, acuminate and measure 6 to 15 cm long and 6 to 25 cm wide. The base is narrowed. The leaves are green, sometimes with a white mid-rib. The stems are smooth, round and dull green permeated with red when young, turning to brownish-grey when matured.

Buds of the Blood Flower.  Note the aphids feeding on the stems
A close up shot of the flower of the Blood Flower
Flowers of the Blood Flower plant in various stages of maturity
The all-yellow flowers of a rarer cultivar of the Blood Flower

The flowers are perfect, radially symmetrical or irregularly shaped, bright red or orange with yellow centres, and measure approximately 12.5 mm. There are five sepals, deeply divided, reflexed and green. There are five petals which are linear with base united into a fused corolla. The corolla lobes are red, reflexed, oblong and approximately 8 mm long. The corona is hood-shaped with inwardly curved horns. There are five stamens. Anthers have two pollen sacs. The style filaments are united with pistils which have two carpels.

A young follicle (seed pod) of the Blood Flower (left) ; and the ripened pod with the Blood Flower seeds all ready to be disperse by the wind

The fruit is a pair of dry dehiscent, spindle-shaped follicles, measuring 5 to 15 cm long. Seed pods are light green and elongated, with approximately 70 to 80 seeds and split lengthways on one side upon maturity. Seeds are ovate and flattened, brown, 6 to 7 mm long, and have a narrow wing completely encircling the margin. Each seed is topped with a coma comprised of silky white hairs, 2 to 3 cm long, that assist in dispersal by wind.

Two forms of the Plain Tiger 

The Blood Flower has medicinal uses. The roots are known as pleurisy root and used as an expectorant for pleurisy, pneumonia, and other lung problems. An extract of the roots has emetic and laxative effect. A poultice of the root is employed to treat ringworm and to stop bleeding. The milky sap of the stems is used to treat warts and skin parasites. A decoction of the plant is used to induce abortion.

A Common Mime feeding on the flower of the Blood Flower

Where the Blood Flower is cultivated, some of the common urban butterflies visit the flowers for its nectar. Amongst the Papilionidae, I have only seen the Common Mime (Papilio clytia clytia) feeding at its flowers. Perhaps the other Swallowtails and Birdwings prefer other nectaring sources than the Blood Flower, but it is also possible that the Common Mime, being a mimic of the Blue and Dark Glassy Tigers, is able to fool predators into avoiding it whilst feeding on this flowering plant with its more distasteful friends.

Tigers Galore!  Various Tigers enjoying the nectar from the flowers of the Blood Flower

The Danainae are often seen on the Blood Flower as a nectaring source, and we have recorded the Common Tiger, Plain Tiger, Black Veined Tiger, Blue Glassy Tiger and Dark Glassy Tiger feeding at the flowers of this plant. Further observations are needed to see if other species of the Danainae also feed on this nectaring plant.

Various Pieridae species feeding on the flowers of the Blood Flower

The urban Pieridae species like the Striped Albatross, Painted Jezebel, Mottled Emigrant and Lemon Emigrant have been photographed feeding on the flowers of the Blood Flower. This plant appears to be a alternative source of nectar for these species of butterflies, although they prefer to feed on other of their preferred flowering plants whenever those are available.

Three Pansies and a Tawny Coster on the flowers of the Blood Flower

Amongst the Nymphalidae, we have observed the Blue, Peacock and Chocolate Pansies using the Blood Flower as a nectaring source. The non-native Tawny Coster is also another regular visitor to this flower.

A female Plain Tiger ovipositing on the leaf of a Blood Flower

Besides being one of the caterpillar host plants of the Plain Tiger, the flowers of the Blood Flower are also a nectaring source for urban butterflies. This plant should be in the landscaping palette of a butterfly garden's designer, as it is certainly a butterfly-attracting plant that is visually attractive and easy to cultivate.

Text by Khew SK : Photos by Sunny Chir, Khew SK, Loh MY and Loke PF.