Butterfly Biodata:
Genus: Catochrysops Boisduval, 1832
Species: panormus C. Felder, 1860
Subspecies: exiguus Distant, 1886
Wingspan of Adult Butterfly: 24-30mm
Caterpillar Local Host Plants: Dendrolobium umbellatum (Fabaceae, common names: Dendulang, Petai Belalang, Petai Laut, Sea Dendrolobium, 伞花假木豆), Pueraria phaseoloides (Fabaceae, common names: Puero, Tropical Kudzu).
Physical Description of Adult Butterfly:
On the upperside, the male is pale shining blue on both forewing and hindwing, and a black marginal spot in space 2 of the hindwing; the female is heavily black dusted with broad black apical area on the forewing, pale bluish wing bases, and the black marginal spot is orange-crowned. On the underside, both sexes are greyish white with the usual streaks and spots. In the hindwing, there is a long filamentous white-tipped black tail at vein 2 and an orange-crowned black spot in space 2. In the forewing, there is a small costal spot which is placed close to the upper end of the postl-discal streak (see picture above).
Field Observations:
The Silver Forget-me-not is moderately rare in Singapore. In the past, the adults were mainly found in open wastelands. However, with the widespread planting of its host plant, Dendrolobium umbellatum, in various parks and gardens, and along several stretches of road in the recent years, adults sightings have become more frequent. At times, several individuals can be seen fighting for the favorite sunbathing spots at some of these locations. The adults fly with an erratic flight, and have been sighted taking nectar at flowering plants. Both sexes have been observed to sunbathe with partly or fully opened wings in sunlit spots. Males also have a habit of puddling on damp footpaths and wet grounds.
Early Stages:
In Singapore, thus far only two larval host plants have been identified. One of them is Pueraria phaseoloides, a twiner and creeping plant commonly found in open wastelands. The other plant is Dendrolobium umbellatum, a shrub or small tree usually found along seashores and in beach forests, but widespread cultivation of this plant has made it a common sight in various gardens, parks and other urban settings. On the host plants, the early stages of the Silver Forget-me-not feed on the flower buds, flowers and developing fruits, with a strong preference for flower buds.
Eggs are laid either singly or in a pair in space between tightly arranged flower buds of the host plant, and are concealed with a transparent gelatinous substance. At times, the egg might be exposed when the growth of flower buds causes them to move further apart. Each bun-shaped egg is about 0.4 to 0.5mm in diameter and whitish in color. It is bun-shaped with a depressed micropylar at the pole and a surface reticulated with rather large polygonal depressions.
It takes about 3 days for the egg to hatch. The young caterpillar consumes just enough of the egg shell to emerge. It is pale greyish brown in coloration, and has a length of about 1mm. Long setae (hairs) run along the length of the body dorsally as well as sub-spiracularly. The head capsule is dark brown to black in coloration. The 1st instar lasts about 3 days with the body length increased to about 1.6mm.
In the 2nd instar caterpillar, in addition to the long setae running along the length of the body dorsally and sub-spiracularly, numerous short setae cover the body surface. The body base colour is pale yellowish green. Pale whitish dorsal bands gradually becomes distinguishable as the second instar progresses. Sub-spiracularly, the body rim is pale whitish. The head capsule remains dark brown to black in coloration, and will be so for the next two instars. The 2nd instar lasts for about 2-3 days, with the body length reaching up to 3.5mm.
In the 3rd instar, the dorsal and sub-spiracular setae appears to be proportionately shorter compared to those in the previous instar. The body is now covered in a dense coat of whitish stellate setae, and the pale whitish dorsal and sub-spiracular bands are more prominent. From the outer sides of the dorsal bands, short bands emanates at the angle, giving an appearance of multiple chevron markings. The body base color ranges from pale yellow green to pale green. The dorsal nectary organ on the 7th abdominal segment is present and barely discernible.
As the body grows to a length of around 6mm, the caterpillar stops feeding and comes to rest at a spot on the underside of a leave or stem to prepare for the next moult. After about 2-3 days in the 3rd instar, the moult to the 4th and final instar takes place.
The 4th instar caterpillar resembles the 3rd instar caterpillar in most body features/markings, but with much contrasting whitish dorsal bands, chevron markings and sub-spiracular band. Thhe dorsal nectary organ on the dorsum of the 7th abdomina segment is now easily discernible, and so is the pair of tentacular organs on the 8th abdominal segment. This 4th (and final) instar lasts about 3-4 days with the body length reaching up to 11mm. On the last day of the 4th instar, the body colour of some individual caterpillars turn reddish brown (red form), while others remains greenish (green form).
As it enters the pre-pupatory phase of its life cycle, the caterpillar ceases its feeding activity. At this time, its body gradually shrinks in length. The pre-pupatory caterpillar typically settles for a spot on a surface which is partially concealed either among foliage of the host plant or in leaf litter. At the chosen pupation site, it spins a silk girdle and a silk pad to which it attaches with claspers at its posterior end.
The pupation event for a Silver Forget-me-not caterpillar.
After about 1 day of the immobile pre-pupatory stage, pupation takes place. The pupa is held firmly via its cremaster to the silk pad. It is 7 to 8mm in length, with the typical shape for a lycaenid pupa. The fresh pupa is either yellow green or pale beige brown, but it will eventually turn pale yellowish to beige brown within first day. The pupa is adorned with multiple black markings of varying sizes and shapes.
About six days later, the pupa becomes darkened in color signaling the imminent emergence of the adult. One can now tell the sex of the soon-to-emerge adult stage from the coloration of the wing pad at this stage (see pictures above). The next day the adult Silver Forget-me-not emerges from the mature pupa.
A male Silver Forget-me-not emerges from its pupal case.
A female Silver Forget-me-not emerges from its pupal case.
References:
- [C&P5] The Butterflies of The Malay Peninsula, A.S. Corbet and H.M. Pendlebury, G. and N. van der Poorten (Eds.), 5th Edition, Malayan Nature Society, 2020.
- Butterflies of Thailand, Pisuth Ek-Amnuay, 2nd Edition, 2012.
- A Field Guide to the Butterflies of Singapore, Khew S.K., Ink On Paper Communications, 2nd Edition, 2015.
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