Life History of the Narrow Spark

Life History of the Narrow Spark (Sinthusa nasaka amba)



Butterfly Biodata:
Genus: Sinthusa Moore, 1884
Species: nasaka Horsfield, 1829
Subspecies: amba Kirby, 1878
Wingspan of Adult Butterfly: 25mm
Caterpillar Host Plants: Eurya acuminata (Theaceae)

Physical Description of Adult Butterfly:
The adults closely resemble adults of Common Tit, a larger and more common species. Above, the male is dark brown on the forewing with deep blue tinge at basal half, and the hindwing is mostly violet blue with a dark brown costal border. The female is dark brown with a white tornal area bearing black spots in the hindwing. Underneath for both sexes, the post-discal line of narrow ochreous brown stripes is mostly continued on the forewing, but broken on the hindwing. A black tornal spot is present in space 2 and another on the lobe of the hindwing, with the tornal area rather sparsely dusted with metallic green scales.

Field Observations of Butterfly Behaviour:
This small species is rather uncommon in Singapore. Sightings have been localized to a few area within the Central Catchment Reserve Area. Encounters with the adults typically take place in dim lighting condition under forest canopy.

Early Stages:

The host plant, Eurya acuminata, is a small tree with lanceolate or ovate-oblong leaves of length 4-9cm. The leaf has finely toothed margin and net-like tertiary veins. The twigs are round and glabrous (finely hairy). The flowers are minute (less than 0.5cm across) and arranged in 2-5 flowered inflorescence, axillary or along leafless twigs. Juice extract of tender leaves is drunk in some parts of the world to relieve dysentery and diarrhoea. Locally, this plant can be found in secondary forest alongside trails within the Central Catchment Reserve Area.


The host plant, Eurya acuminata, pictured with one female Narrow Spark trying to oviposit on the leaf underside

Eggs are laid singly on the a flower bud or on the stem/leaf adjacent to the buds. Each egg is green in color, small (about 0.4-0.5mm in diameter) and circular with a slightly depressed micropylar. The surface is finely sculptured with intersecting ridges. The egg is almost identical to eggs of Rapala species described in the literatures.

A female Narrow Spark ovipositing near a flower bud of the host plant

An egg of the Narrow Spark, about 0.5mm in diameter.

Three days later, the egg hatches with the young caterpillar eating away the upper portion of the egg shell to emerge. Measured at a length of about 0.8-0.9mm, it is cylindrical in shape, sporting long setae (hairs), a large dark brown head capsule and overall pale yellow body.

Mature egg (left), empty egg shell (right)

1st instar caterpillar, newly hatched, length: about 0.8mm

The 1st instar caterpillar bores into a flower bud and eats the developing flower parts within it. It feeds with its head in first, keeping its rear end close to the entrance for ejecting frass outside the bud. Usually the presence of caterpillar "hidden" in a particular hole is given away by tuffs of fine hair at the hole entrance and the presence of frass nearby.

Left to right, a 1st instar caterpillar re-entering a flower bud for its feast, length: 1.2mm

After 2 days of growth and reaching a length of about 2mm, the caterpillar moults to the next instar. Some caterpillars actually moult within a flower bud. The second instar caterpillar has numerous tubercles covering its body with short fine hairs protruding from them. There are small dark brown spots set against a light brown base color. As the caterpillar grows larger, more and more of the posterior end of its body will remain outside the flower bud as it feeds on the goodies within.


2nd instar caterpillar, late in this stage, length:4mm

The 2nd instar caterpillar reaches a length of about 4.5mm, and after 3 days in this stage, it moults again. Keeping a similar appearance as in previous instar, the 3rd instar caterpillar has more prominent dorsal markings with a brown dorsal line. Tubercles lining the body segments in the sub-dorsal and sub-spiracular locations have become enlarged with tuffs of protruding setae. The typical lycaenid nectary organs (both the dorsal nectary organ and tentacular organs) are now discernible. The 3rd instar takes 3 days to complete with the body length reaching about 8.5mm.


3rd instar caterpillar checking out a flower bud, length: 8mm

The 4th (and final) instar caterpillar still has the same dorsal markings as in earlier instars, but the white diamond-shaped prothoracic shield now has prominent black spots at its 4 corners. Initially the body base color is pale brown with the 1st thoracic segment and the anal plate yellowish green. As the caterpillar grows, as depicted in the 3 figures below, the base color changes to yellowish brown and finally to yellow in the first three days of this instar. The sub-dorsal and sub-spiracular rows of tubercles become translucent to transparent in appearance, with some of them assuming a bluish coloration. Furthermore, as the body base color changes to yellow, the 5th abdominal segment also becomes darkened from the sub-dorsal to sub-spiracular area.

4th instar caterpillar, day 1 of 5 in this stage, length: 10mm


4th instar caterpillar, day 2 of 5 late in this stage, 12mm

4th instar caterpillar, day 3 of 5 in this stage, 14mm

The dorsal nectary organ and the tentacular organs on the 7th and 8th abdominal segments respectively are rather prominent in the final instar caterpillar. On the last day of the final instar, copious amount of clear fluid was observed to be excreted from the nectary organs of the shortened and decolorized caterpillar. These functioning nectary organs suggest a strong caterpillar-ant association in the wild.

The anterior segments of a 4th instar caterpillar, the nectary organs are annotated.

After five days of growth and reaching a maximum length of around 14mm in the the final instar, the body of the caterpillar becomes shortened and decolorized caterpillar. Soon it chooses a spot on the leaf surface to remain stationary and becomes a pre-pupatary larva. At this site, it prepares for pupation by spinning a silk girdle and a silk pad to which it attaches itself via cremastral hooks.


A pre-pupa of the Narrow Spark, showing a finished silk girdle securing it to
the leaf surface, also visible is clear fluid from a final purge.

Pupation takes place after 1 day of the pre-pupa stage. The hairy pupa has a shape typical of most lycaenid species, and a length of about 7.5mm. It is light brown dotted with small dark brown specks.


Two views of a pupa of the Narrow Spark.

Seven days later, the pupa becomes darkened in color signaling the imminent emergence of the adult. The uppersides of the forewings become visible through the now transparent pupal skin, allowing one to tell the gender of the soon-to-appear adult. The next day the adult butterfly emerges from the mature pupa.


Two views of mature pupa of the Narrow Spark


A newly eclosed female Narrow Spark resting on a perch


A male Narrow Spark resting on a perch in CCA

Acknowledgments:

I would like to express my gratitude to Prof Hugh Tan of NUS DBS and Ali Ibrahim of Nparks for providing confirmation of the host plant species ID.


References:

• The Butterflies of The Malay Peninsula, A.S. Corbet and H.M. Pendlebury, 4th Edition, Malayan Nature Society.
• The Butterflies of Hong Kong, M. Bascombe, G. Johnston, F. Bascombe, Princeton University Pres 1999

Text and Photos by Horace Tan