31 August 2013

Life History of the White Palm Bob

Life History of the White Palm Bob (Suastus everyx everyx)

Butterfly Biodata:
Genus: Suasus Moore, 1881
Species: everyx Mabille, 1883
Sub-species: everyx Mabille, 1883
Wingspan of Adult Butterfly: 24-28mm
Caterpillar Local Host Plant: Daemonorops augustifolia (Arecaceae; common name: Water Rattan Palm).

Physical Description of Adult Butterfly:
The adults are diminutive in size. Above, the wings are brown and typically unmarked. In some female specimens, small white spots might be present in space 2 and the cell in the forewing. In the hindwing, the tornal area and tornal cilia are white. Underneath, the wings are brown and overlaid with buff scaling. In the hindwing, the lower two-thirds are white with several dark spots of varying sizes. The abdomen is brown and white banded.

Field Observations of Butterfly Behaviour:
The White Palm Bob is rare in Singapore. Sightings are rather localized to a forested area in a reservoir park. They are usually found flying in the deep shaded area near ground level. At times, they are also sighted puddling on wet ground and on bird droppings.

Early Stages:
Thus far only one local host plant, the Water Rattan Palm, has been established for White Palm Bob. This plant is rather common in the forested area where the species resides. The caterpillars feed on leaves of the host plant and live in leaf shelters. In all instars, the caterpillar builds tent-like shelter on the underside of a leaflet by cutting and joining leaf fragments. As the caterpillar grows in size later through progressing instars, it will construct ever larger shelters. In the final instar, two adjacent leaflets are typically used as a larger shelter is necessary for housing the much larger larval body.

Local host plant: Daemonorops augustifolia (Water Rattan Palm).

The eggs are laid singly on the upper surface of a leaflet of the host plant. Each shallow dome-shaped egg is wine red with yellowish to whitish longitudinal ridges emanating from the polar region where the micropylar is sited. The eggs are rather small with a diameter of about 1mm.

A far view of an egg laid on the leaflet of the Water Rattan Palm.

Two views of an egg of the White Palm Bob, diameter: 1mm.

It takes about 4 days for the egg to hatch. The egg decolorises to yellowish brown colour when fully mature on the last day of this phase. The young caterpillar eats just enough of the shell to emerge. Its golden yellow body has a length of about 2mm. There is a tuff of moderately long setae on the posterior segment. The head is comparatively large and is yellowish brown in colour.

A sequence of three views of a mature egg on the last day of the oval stage.

Two views of a newly hatched caterpillar taking a bite of its egg shell.

Two views of a newly hatched caterpillar, length: 2.1mm.

After emerging from the egg, the caterpillar makes only a weak attempt at eating the egg shell remnant before moveing on to the leaf edge to construct its first leaf shelter. Its body takes on a slight green undertone after a few feeding sessions near its shelter. The 1st instar takes a total of 3 days to complete with body length reaching about 4mm.

Two views of a 1st instar caterpillar, length: 3.6mm.

Top: the leaf shelter of a 1st instar caterpillar. Bottom: the same leaf shelter opened to show the resident caterpillar.

The body of the 2nd instar caterpillar is yellow with a green undertone and the head capsule is pale yellowish brown. The tuff of moderately long setae at the posterior end is now absent, being replaced by a few short setae. This instar lasts a total of 3-4 days with the body length reaching up to 6mm.

A newly moulted 2nd instar caterpillar, length: 3mm.

Two views of a 2nd instar caterpillar, length: 5.5mm.

In the 3rd instar, the body colour decolorises from yellow to whitish as growth progresses. The head is paler in coloration compared to the earlier instars. This instar lasts a total of 4-5 days with the body length reaching 8-9mm.

Top: late 2nd instar caterpillar, dormant prior to its moult. Bottom: newly moulted 3rd instar caterpillar.

Two views of a 3rd instar caterpillar, length: 7mm.

The 4th instar ushers in an obvious change in the head capsule where the base colour is now pale brown to white and there are numerous brown spots dotting the lateral sides. The body is also adorned with numerous tiny, white spots and a faint, narrow, whitish, lateral band runs along lengthwise. This penultimate instar lasts 4-5 days with the body length reaching 12-14mm.

Top: leaf shelter of a White Palm Bob caterpillar. Middle: the same leaf shelter opened to review a late 3rd instar caterpillar. Bottom: the same caterpillar newly moullted to the 4th instar.

Two views of a 4th instar caterpillar, length: 11mm.

As in the 4th instar, the body of the 5th instar caterpillar is mostly translucent with numerous, tiny, white spots and has a white lateral band running lengthwise. The head capsule is also similar to those in the 4th instar except that the contrast between white base colour and the brown spots are now much more prominent. The periphery of the head capsule is marked in brown.

Top: leaf shelter of a White Palm Bob caterpillar. Middle: the same leaf shelter opened to review a late 4th instar caterpillar. Bottom: the same caterpillar newly moullted to the 5th instar.

Two views of a 5th instar caterpillar, late in this stage, length: 21mm.

The 5th instar takes about 7-8 days to complete with the body length reaching 21-22mm. In the last 1-2 days of this instar, the caterpillar seeks out a new site on a leaflet to construct its leaf shelter. Within the pupation shelter, a large amount of silk threads are spun and a great mass of whitish powdery substances are secreted to coat the inner surface of the shelter. Typically the pupation shelter is cut from the leaflet before the caterpillar proceeds to seal the shelter. This prepupatory phase lasts for 1.5-2 days.

Top: a detached pupation shelter. Bottom: the same shelter opened to reveal a fresh pupa.

Pupation takes place within the leaf shelter. The pupa does not have a cremastral attachment nor a silk girdle. The body is pale green in the thorax and wing pad areas, but yellow in the abdomen. As is common in the case of pupation within a closed shelter for skipper species, purged frass pallets and the exuvia and head capsule of the final instar caterpillar can be found near the posterior end of the pupa. Length of pupae: 13.5-15mm.

Two views of a pupa of the White Palm Bob, length: 13.5mm

After 8 days, the pupa becomes mostly dark brown to black as the adult development stage within its case comes to an end. Eclosion takes place the next day.

Two views of a mature pupa of the White Palm Bob.

A newly eclosed White Palm Bob.

  • [C&P4] The Butterflies of The Malay Peninsula, A.S. Corbet and H.M. Pendlebury, 4th Edition, Malayan Nature Society.
  • Butterflies of Thailand, Pisuth Ek-Amnuay, 2nd Edition, 2012
  • A Field Guide to the Butterflies of Singapore, Khew S.K., Ink On Paper Communications, 2010.
Text by Horace Tan, Photos by Nelson Ong, Loke PF, Federick Ho, Sunny Chir, Khew SK and Horace Tan.

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