13 June 2020

Life History of the Malay Staff Sergeant

Life History of the Malay Staff Sergeant (Athyma reta moorei)


Butterfly Biodata:
Genus: Athyma Westwood, 1850
Species: reta Moore, 1858
Subspecies: moorei Fruhstorfer, 1906
Wingspan of Adult Butterfly: 50-60mm
Caterpillar Local Host Plant: Glochidion zeylanicum (Phyllanthaceae).


A female Malay Staff Sergeant enjoying a good meal on the ripened fruits of the Singapore Rhododendron.

A male Malay Staff Sergeant puddling on wet ground.

A male Malay Staff Sergeant with closed wings giving a view of its underside.

Physical Description of Adult Butterfly:
Forewing cell is closed. Malay Staff Sergeant is sexually dimorphic with a black-and-white (white markings on black background) male and a black-and-orange female. On the forewing upperside, the cell streak is twice-constricted, and the arrowhead-shaped marking beyond the cell streak is well apart in the male. The cell streaks of the left and right forewings are connected via a dorsal band on the thorax. The post-discal spots in spaces 4, 5 and 6 are well separated in the male but confluent in the female. There is no post-discal spot in space 3 in the male but there is a small one in the female. The post-discal spot in space 2 is oval and well separated from that in space 1b in the male, but is oblong and adjoining the spot in space 1b in the female. On the hindwing upperside, there are sub-discal band, post-discal band and marginal band which run from the costa to the dorsum. On the underside, the spots and streaks are arranged as on the upperside but with the ground colour yellowish to dark brown.


Another male Malay Staff Sergeant puddling on wet ground.

A female Malay Staff Sergeant bathing in the sun on the leaves of its host plant Glochidion zeylanicum.

A female Malay Staff Sergeant with closed wings giving a view of its underside.

Field Observations of Butterfly Behaviour:
The Malay Staff Sergeant is a uncommon butterfly in Singapore. The strong and fast-flying adults can be sighted at the fringe of nature reserves, and several forested wastelands across the island. The adults visit flowers and ripened fruits for the sugary contents. The male has been sighted puddling on wet grounds.

A video record of the life history of the Malay Staff Sergeant.

A sun-bathing male Malay Staff Sergeant sighted in the western region of Singapore.

Another male Malay Staff Sergeant sighted in the western region of Singapore, resting on a flower of Bidens alba.

A newly eclosed female Malay Staff Sergeant.

Early Stages:
Only one host plant, Glochidion zeylanicum, has been recorded as larval hosts for the Malay Staff Sergeant in Singapore so far. It is likely that other Glochidion species could serve as larval hosts, as in the case of the closely related Athyma nefte (Colour Sergeant).

Local host plant: Glochidion zeylanicum.

The caterpillars of the Malay Staff Sergeant adopt the same feeding and frass management routines as described for other Athyma species in earlier blog articles. The caterpillars feed on mature leaves of the host plant in all five instars of its development. On each leaf, they feed systematically from the leaf tip towards the petiole, leaving the midrib intact. From the 1st to the 4th instar, they build an extension of the exposed midrib using frass pellets held together by silk. Frass pellets are also sewn together beneath the midrib at the base of the extension. The caterpillars rest on either the frass extension or the exposed midrib above the bundle of frass pellets there. In the 5th (and final) instar, the caterpillars abandon these habits, resting on the leaf upperside and feeding irregularly from the leaf margin.

A mating pair of the Malay Staff Sergeant. Top: male; Bottom: female.

The eggs of the Malay Staff Sergeant are laid singly at the tip of a leaf of the host plant. Each dome-shaped egg is yellow in colour, with its surface marked with polygonal ridges which are tipped with fine, translucent spines at intersections of these ridges. Basal diameter is approximately 1.0mm.

A female Malay Staff Sergeant ovipositing at the tip of a leaf of Glochidion zeylanicum.

A time-lapse sequence of a female Malay Staff Sergeant ovipositing at the tip of a leaf of Glochidion zeylanicum.

Two views of an egg of the Malay Staff Sergeant.

The egg takes about 3 days to hatch. The young caterpillar nibbles away a portion of the egg shell to exit and then proceeds to devour the rest of the egg shell. It has a cylindrical body in pale, dull brown, and an initial body length of about 2.2mm. The body is covered with fine setae, and dorso-lateral, lateral and sub-spiracular tubercles. The head is brown in colour.

Two views of a fully developed egg of the Malay Staff Sergeant.

A newly hatched caterpillar of the Malay Staff Sergeant eating its egg shell.

Two views of a newly hatched caterpillar, length: 2.2mm.

An early 1st instar caterpillar of the Malay Staff Sergeant, observed in the field, resting on the frass extension a few hours after hatching.

Soon after its emergence, it feeds on the leaf lamina around the midrib, and builds an extension of the exposed midrib using frass pellets sewn together with silk. The first instar lasts about 3 days with the body length increases to about 4.8mm.

Two views of an early 1st instar caterpillar, resting at the base of the frass extension, length: 2.5mm.

Two views of a late 1st instar caterpillar, length: 4.8mm.

In the 2nd instar, the dorso-lateral, lateral and sub-spiracular tubercles have short, branched setae. An obscure, pale brown diamond-shaped dorsal patch stretches from the 5th abdominal segment to the 4th abdominal segment, and a similar coloured triangular dorsal patch extend from the 3rd abdominal segment to the 4th abdominal segment. The dark brown head is adorned with short pale brown tubercles and peripheral spines. The 2nd instar lasts about 2 days with the body length reaches about 7.0mm.

Two views of a 2nd instar caterpillar, newly moulted, length: 4.2mm.

Two views of a 2nd instar caterpillar, length: 5.8mm.

Two views of a late 2nd instar caterpillar, dormant prior to its moult, length: 7mm.

A 2nd instar caterpillar of the Malay Staff Sergeant, observed in the field, resting on the exposed midrib.

Another 2nd instar caterpillar of the Malay Staff Sergeant, observed in the field, resting on the exposed midrib.

The 3rd instar caterpillar mostly resembles the the second instar caterpillar, but with the body tubercles, setae and the head spines longer and more prominent. The body and the head are now much darker, and pale brown dorsal patches more distinct. Another pale brown triangular dorsal patch appears from the 3rd thoracic segment to the 1st abdominal segment. There are also whitish sub-spiracular processes from the 7th to 9th abdominal segments. This instar takes about 2 days to complete with body length reaching about 10.5mm.

Two views of a 3nd instar caterpillar, early in this stage, length: 7mm.

Two views of a 3nd instar caterpillar, length: 10.5mm. Inset: head.

Two views of a late 3nd instar caterpillar, dormant prior to its moult, length: 10.3mm.

A 3rd instar caterpillar of the Malay Staff Sergeant, observed in the field, resting on the exposed midrib.

The 4th instar caterpillar has distinctly longer dorso-lateral branched setae in the 2nd and 3rd thoracic segments than the other setae. Peripheral head spines are longer than those in the previous instar. The anterior two dorsal patches are initially brown, but turning green in the latter part of the instar. The dorsal patch in the 5th abdominal segment is reddish brown. The 4th instar lasts about 3 days with body length reaching about 15mm.

Two views of a 4th instar caterpillar, early in this stage, length: 10.5mm.

Two views of a 4th instar caterpillar, length: 10.5mm. Inset: head.

Two views of a late 4th instar caterpillar, length: 15mm.

The next moult brings the caterpillar to its 5th and final instar. Now the dorso-lateral setae are alongated and branched distally and peripheral spines on the head becomes much more pointed. The body colour is initially brown, but turning green within a day. At the same time, the dorso-lateral and lateral processes turn reddish, and the anterior two dorsal patches disappear. The dorsal patch on the 5th abdominal segment is rectangular, black initially but turning purplish to reddish brown as the body turns green. The head is dark brown to black, with off-white or pale pinkish front stripes flanking the adfrontal suture. Tubercles present on the head are of the same colour as the frontal stripes.

The heads of two 5th instar caterpillars, showing the two different colorations of stripes and tubercles.

Two views of a newly moulted 5th instar caterpillar.

An early 5th instar caterpillar of the Malay Staff Sergeant sighted in the field.

Two views of an early 5th instar caterpillar, with the body colour transiting to green.

Two views of a 5th instar caterpillar, with the body colour transition completed, length: 27mm. Inset: head.

Two views of a 5th instar caterpillar, length: 32mm.

Towards the end of the 5th instar, the body ground colour changes to yellow and then pale beige, with pale blue to dark blue markings appearing on all body segments. The tubercles one the head also turn bluish. The 5th instar lasts about 4-5 days, with the body length reaches up to 32mm. On the last day, the caterpillar ceases feeding and seek out a spot on the underside of a leaf (usually on the midrib) or rarely a stem/branch to spin a silk pad. It then anchors itself there via its posterior end, and assumes its upside-down pre-pupatory pose.

Two views of a 5th instar caterpillar, late in this stage, length: 32mm.

Two views of a prep-pupa of the Malay Staff Sergeant. Left: early; Right: late.

After one day of the immobile pre-pupatory phase, the transformation process to the pupal phase takes place. The pupa has cephalic protuberances with their apices extended laterally. There are also dorsal protuberances on the first thoracic segment and the first abdominal segment which are long and keeled, and pointed towards each other. The pupa is initially pale biege brown but turning orange-brown with golden patches a few hours later. Length of pupae: 22-23.5mm.

Three views of a pupa of the Malay Staff Sergeant.

After about 6 days of development, the pupa becomes darkened in color, and the spots/streaks on the forewings are visible through the pupal skin in the wing pads. The next day the eclosion event takes place with the adult butterfly emerges to start the next phase of its life cycle.

Three views of a fully developed pupa of the Malay Staff Sergeant.

The eclosion events of both male and female Malay Staff Sergeant.

A newly eclosed female Malay Staff Sergeant.

A newly eclosed male Malay Staff Sergeant.


References:
  • Discovery of the previously overlooked female of Athyma reta, and its taxonomic implications, L.G Kirton, H. Tan, C-K Phon and S.K. Khew, Raffles Bulletin of Zoology, vol. 68, pp.249-266.
  • [C&P4] The Butterflies of The Malay Peninsula, A.S. Corbet and H.M. Pendlebury, 4th Edition, Malayan Nature Society, 1992.
  • 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 Sunny Chir, Khew SK and Horace Tan