14 April 2012

Life History of the Striped Blue Crow

Life History of the Striped Blue Crow (Euploea mulciber mulciber)

Butterfly Biodata:
Genus: Euploea Fabricius, 1807
Species: mulciber Cramer, 1777

Subspecies: mulciber Cramer, 1777
Wingspan of Adult Butterfly: 80-90mm
Caterpillar Local Host Plants: 
Calotropis gigantea (Asclepiadaceae, common name: Giant Milkweed), Gymnanthera oblonga (Apocynaceae, common name: Sea Rubber Vine), Nerium oleander (Apocynaceae, common name: Oleander), and various members of the Ficus genus including Ficus microcarpa (Moraceae, common name: Chinese Banyan), F. grossularioides (common name: White-leafed Fig) and F. lamponga.

A female Striped Blue Crow  visiting a flower of Bidens alba.

Another female  Striped Blue Crow visiting a cluster of Lantana flowers.

A sunbathing male Striped Blue Crow displaying its upperside.

Physical Description of Adult Butterfly:
Above, the male is bright blue in the forewing with diffuse white spots in the distal half; while the female is blue with embedded white spots in the distal half of the forewing and several white spots and streaks in the brown basal half. Both sexes have a brown hindwing  with the female having additional narrow white streaks arranged as per the Ideopsis species.  Underneath, the wings are brown with white spots/streaks arranged similarly to those on the upperside though with variation in size of the spots/streaks.

A  female Striped Blue Crow feeding on  Syzygium flowers in an open-wing posture.

A male Striped Blue Crow visiting Syzygium flowers.

Another male Striped Blue Crow on a leaf perch.

Field Observations of Butterfly Behaviour:  
The sexually dimorphic Striped Blue Crow is the most common Crow species in Singapore. Though not abundant, the adults have been observed in many locations, including the nature reserves, mangrove habitats,  wastelands and even in urban parks and gardens. The adults are attracted to flowers, and are easiest to approach for photo-taking when they are occupied during their flower visits.  

Early Stages:
The Striped Blue Crow is polyphagous and has many larval host plants in the Moraceae, Apocynaceae and Asclepiadaceae families.  The fact that it can utilize some many hosts which grow in multiple types of habitats account for its wide distribution  and the common status in Singapore. The caterpillars of Striped Blue Crow feed on leaves and young shoots of the host plants, typically with the early instars focusing on  young tender leaves and  later instars moving on to the more mature leaves. The caterpillar has the habit of first cutting the mid-rid or the petiole of a leaf  before eating the leaf lamina beyond the severed point. A web of silk threads helps to secure the severed or nearly severed part.

Local host plant: Ficus microcarpa.

Local host plant: Gymnanthera oblonga.

A mother Striped Blue Crow laying egg on the underside of a young leaf of F. microcarpa.

The eggs of the Striped Blue Crow are laid singly on the underside of a leaf (typically young leaf) of the host plant. The creamy yellow eggs are tall (about 1.8-1.9mm in height) and somewhat cylindrical (diameter: 1.2mm) with a rounded top. The egg surface is ribbed.

Two views of an egg of the Striped Blue Crow.

Two views of a mature egg of the Striped Blue Crow.

The egg takes about 3 days to hatch. The young caterpillar emerges by eating away part of the egg shell. The rest of the egg shell becomes the first meal for the newly hatched, which has a length of about 3.2mm. The newly hatched has a pale yellowish  body and black legs. The large head capsule is black in color. A pair of very short and inconspicuous protuberances can be found on the dorsum of each of the following four segments: 2nd and 3rd thoracic segments, the 2nd and 8th abdominal segments.

Two views of a newly hatched caterpillar, length: 3.2mm.

Once the newly hatched moves on to feed on the leaf lamina, its body starts to take on a green undertone. The newly hatched has this interesting  habit of marking out a  portion of the leaf with  a series of small spots before eating away the marked out portion. In the final half day of the 1st instar, the body takes on yellowish brown transverse stripes on all segments. This instar lasts for 2-2.5 days with the  the body length doubled up to 7 mm.

Two views of a 1st instar caterpillar,  length: 5mm

Two views of a 1st instar caterpillar, late in this stage, length: 6.9mm.

The body of the 2nd instar caterpillar has a yellow ground color. There are dark brown  transverse rings interspersed with whitish stripes on each of the body segments except for the very 1st segment. The most obvious change is the lengthening of the 8 tiny protuberances seen in the 1st instar to short processes, each of which is almost entirely dark brown to black. There are two small black spots on the dorsum of the prothorax, and one large black patch (anal plate) on the posterior end of the body. This instar lasts only 1.5 days with the body length reaching 12mm before the moult to the 3rd instar.

Two views of a 2nd instar caterpillar, early in this stage, length: 7.5mm

Two views of a 2nd instar caterpillar, length: 9mm

The 3rd instar caterpillar is similar in appearance to the 2nd instar caterpillar with the only obvious change being the proportionally longer processes. Less obvious is the lengthening of a whitish transverse stripe on each segment to below the sub-spiracular area.  In some specimens, two faint whitish lateral streaks appear on the black head capsule. This instar takes about 1.5 days to complete with body length reaching up to 16-18mm.

Top: Late L2 prior to the moult. Bottom: newly moulted 3rd instar caterpillar, length: 11.5mm.

Two views of a 3rd instar caterpillar, length: 13.5mm.

Compared to the 3rd instar, the 4th instar caterpillar has proportionally longer processes.  On the body segments, the transverse white stripes are now prominent with one stripe being broader on the dorsum of each abdominal segment. The lower end of a white transverse stripe on each of the first seven abdominal segment is  constricted to form a white triangular patch.  The black head capsule features two frontal, and oblique  white stripes and  an outer peripheral white ring. This instar lasts 1.5 to 2 days with the body length reaching about 24-28mm.

Top: Late L3 prior to the moult. Bottom: newly moulted 4th instar caterpillar, length: 17mm.

Two views of a 4th instar caterpillar, length: 28mm.

The 5th instar caterpillar again has proportionately longer processes. An obvious change is in  the basal third or quarter of each process being coloured carmine in place of dark brown/black. Another change is in the head capsule where the frontal and peripheral white stripes are now much broader and joined.The white and dark-colored transverse stripes dominate the body surface so much that the yellow coloration is only confined to the prothorax, small lateral patches and the posterior segment.

Two views of a 5th instar caterpillar, length: 34mm.

The Striped Blue Crow caterpillar, unlike the Blue Spotted Crow (E. midamus singapura) and the King Crow (E. phaenareta castelnaui), does not have an adenosma (or prostenal gland, located just ahead of the 1st pair of thoracic legs). When the caterpillar was  intentionally agitated, no eversion of any structure can be seen (at the expected location) in multiple observations. The caterpillar merely adopted a head-tugged defensive stance in such occasions.

A 5th instar caterpillar found in the nature reserve on Ficus lamponga, adopting a defensive stance.

In some specimens, the colour change to carmine in the basal part of the processes  also extend to the dark brown transverse stripes on the body segments and even to the head capsule. In another colour variant, the usual bright yellow coloration on body markings is replaced by  a pale shade of  yellow.

Two views of a 5th instar caterpillar with more extensive carmine coloration length: 29mm.

Two views of a 5th instar caterpillar, late in this instar,  length: 43mm.

Two views of a 5th instar caterpillar, with more extensive carmine and paler yellow coloration, late in this instar,length: 46mm.

The 5th instar lasts for 3.5-4 days, and the body length reaches up to 51-53mm. On the last day, the caterpillar ceases feeding, and its body becomes shortened and decolorised to a shade of pale beige brown. For pupation, the caterpillar typically chooses a spot on the mid-rib of a leaf underside. At this pupation site, the caterpillar spins a silk pad from which it then hangs vertically to take on the pre-pupatory pose.

A pre-pupatory larva of the Striped Blue Crow.

Pupation takes place 0.5 days after the caterpillar assumes the hanging posture. The pupa  suspends itself from the silk pad with no supporting silk girdle. Initially, the pupa is in a light shade of yellowish brown, but the surface gradually takes on a silvery metalic glitter about a day later. The pupa is rather rotund, and has a few tiny black spots  on the dorsum. Length of pupae: 19-21mm.

Three views of a fresh pupa of the Striped Blue Crow, several hours after pupation.

Three views of a shining pupa of the Striped Blue Crow, one day  after pupation.

Three views of a mature pupa of the Striped Blue Crow, night before eclosion.

After about 6-7 days of development, the pupal turns black as the development within the pupal case comes to an end. The white spots on the forewing upperside become discernible through the now translucent skin. In the following morning, the adult butterfly emerges from the pupal case, and  perches nearby to expand and dry its wings before taking its first flight.

A newly eclosed male Striped Blue Crow drying its wings on its pupal case.

A newly eclosed female Striped Blue Crow drying its wings on its pupal case.

  • [C&P4] The Butterflies of The Malay Peninsula, A.S. Corbet and H.M. Pendlebury, 4th Edition, The Malayan Nature Society.
  • Butterflies of Thailand, Pisuth Ek-Amnuay, 1st Edition, 2006
  • A Field Guide to the Butterflies of Singapore, Khew S K, Ink on Paper Comm. Pte. Ltd, 2010.
Text by Horace Tan, Photos by Benedict Tay, Federick Ho,  Sunny Chir, Khew SK  and Horace Tan