29 June 2021

Life History of the Silver Forget-me-not

Life History of the Silver Forget-Me-Not (Catochrysops panormus exiguus)


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).


A Silver Forget-me-not visting flowers for nectar.

The upperside of a male Silver Forget-me-not.

A main identification key of the Silver Forget-me-not.

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).

The upperside of a female Silver Forget-me-not.

A female Silver Forget-me-not taking nectar from a flower of Cuphea hyssophifolia 'Pink' (False Heather).

A male Silver Forget-me-not perching on a stem of Dendrolobium umbellatum.

A male Silver Forget-me-not puddling on wet ground.

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.

A female Silver Forget-me-not taking nectar from a flower of Tridax procumbens (Coat Buttons).

A puddling male Silver Forget-me-not.

A male Silver Forget-me-not found probing a leaf surface with its proboscis.

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.

Local host plant #1: Dendrolobium umbellatum (Fabaceae, common names: Dendulang, Petai Belalang, Petai Laut, Sea Dendrolobium, 伞花假木豆).

Local host plant #2: Pueraria phaseoloides (Fabaceae, common names: Puero, Tropical Kudzu).

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.

A Silver Forget-me-not female searching for a spot to lay egg on Dendrolobium umbellatum.

A Silver Forget-me-not female laying an egg on Pueraria phaseoloides.

A freshly laid egg of the Silver Forget-me-not among the flower buds of Dendrolobium umbellatum. Concealed within a transparent gelatinous substance indicated by the arrow.

An egg of the Silver Forget-me-not.

Left: A fully developed egg. Right: The newly hatched caterpillar resting next to the empty egg shell.

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.

Two views of a newly hatched caterpillar, length: 1mm.

A 1st instar caterpillar feeding on a flower bud of Dendrolobium umbellatum. Note that pile of frass pellets near the posterior end of the caterpillar.

Two views of a 1st instar caterpillar, length: 1.6mm.

A late 1st instar caterpillar of the Silver Forget-me-not, dormant prior to the moult to the next instar.

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.

Two views of a newly moulted 2nd instar caterpillar, with its old skin next to its posterior end.

Two views of a 2nd instar caterpillar of the Silver Forget-me-not, length: 3mm.

A 2nd instar caterpillar of the Silver Forget-me-not feeding on a flower bud of Dendrolobium umbellatum.

Two views of a 2nd instar caterpillar, late in this stage, dormant prior to its moult.

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.

Top: late 2nd instar caterpillar; bottom: newly moulted to 3rd instar, its old skin lying at the posterior end.

Two views of an early 3rd instar caterpillar feeding on a flower bud, length: 4.1mm.

Two views of a 3rd instar caterpillar, length: 5mm.

A 3rd instar caterpillar found in the field feeding on a seed pod of Dendrolobium umbellatum.

Two views of a late 3rd instar caterpillar on the underside of a leaf, dormant prior to its moult to the next instar, length: 5.3mm.

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.

Two views of a very late 3rd instar caterpillar, dormant prior to its moult to the final instar.

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).

Two views of a newly moulted 4th instar caterpillar (the same individual featured in the above picture).

Frontal view of a 4th instar caterpillar, showing the dark brown head.

A 4th instar caterpillar found in the field feeding on a flower of Dendrolobium umbellatum.

Two views of a 4th instar caterpillar, length: 9mm.

A 4th instar caterpillar found in the field with ants in attendance.

Two views of a late 4th instar caterpillar, red 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.

Two views of a pre-pupa of the Silver Forget-me-not, red form.

Two views of a pre-pupa of the Silver Forget-me-not, green form.


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.

Two views of a newly formed pupa of the Silver Forget-me-not from the red-form pre-pupa.

Two views of a newly formed pupa of the Silver Forget-me-not from the green form pre-pupa.

Two views of a pupa of the Silver Forget-me-not, length: 7mm.

Two views of a mature pupa of a female Silver Forget-me-not.

Two views of a mature pupa of a male Silver Forget-me-not.

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.

A newly eclosed male Silver Forget-me-not resting next to 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.
Text by Horace Tan; Photos by Loh Mei Yee, Lim Cheng Ai, Sunny Chir, Nelson Ong, Khew SK and Horace Tan; Videos by Loh Mei Yee and Horace Tan.

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