Life History of the Cabbage White

Life History of the Cabbage White (Pieris canidia canidia)

Butterfly Biodata:
Genus: Pieris Schrank, 1801
Species: canidia Linnaeus, 1768
Subspecies: canidia Linnaeus, 1768
Wingspan of Adult Butterfly: 45-55mm
Caterpillar Local Host Plant: Cleome rutidosperma (Capparaceae, common name: Purple Cleome, Fringed Spiderflower).

A male Cabbage White.

Physical Description of Adult Butterfly:

The wings are mostly white, and dusted in black (more heavily so in the basal areas of both fore- and hindwings). On the upperside, the forewing sports a black apical border and a black post-discal spot in space 3. On the hindwing, there is a black sub-costal spot and four to five black marginal spots. The female is more heavily marked in black than the male, and has a distinct double spot in space 1b of the forewing. On the underside, the wings are mostly white in the male, and strongly yellow-dusted in the female (in the hindwing and the apical area of the forewing). In both sexes, there is a yellow basal streak along the costa on the hindwing, and there are black post-discal spots in spaces 1b, 3 and 5 in the forewing. The spot in space 5 is typically much less conspicuous than the other two.

A female Cabbage White.

Field Observations of Butterfly Behaviour:

This species occurs in open grassy areas and flies in the company of the Striped Albatross and Psyche, both of which share the same local host plant with the Cabbage White. It is a weak flyer, and keeps close to the ground looking for flowers to feed on. On sunny days, it flies restlessly, and rarely stops for long. The species can occasionally be found in wastelands, farm ways and parklands and is sometimes common where it occurs. Often, several individuals are seen at one time, especially in the vicinity of the host plant. The males have the habit of puddling for mineral intakes. Although C&P4 described the Cabbage White as not uncommon in Singapore, sightings of this species, however, have become much less frequent in the past years.

Early Stages:

The recorded local host plant for the Cabbage White, Cleome rutidosperma, is a common herbaceous weed with violet-blue to pink flowers. Caterpillars of the Cabbage White feed on the relatively young to middle-aged leaves as well as young shoots, stems and flower parts. A noteworthy feature is that caterpillars of Cabbage White, in all instars, possess a prosternal gland, on the ventrum of the prothorax. This gland is present in a limited number of butterfly species,and it is everted when the caterpillar is roughly handled. Past studies have found it is capable of emitting chemicals with a defensive function.

The prosternal gland (on the ventrum behind the head) of a Cabbage White caterpillar.

Local host plant: Cleome rutodosperma.

A mating pair of the Cabbage White.

A Cabbage White laying an egg on a leaflet of the host plant.

Eggs of the Cabbage White are laid singly on a leaf of the host plant. The pale yellowish egg is cylindrically-shaped with a narrowing upper end, and has a height of about 1mm. It has vertical ridges and numerous transverse striations. The vertical ridges end in low projections encircling the micropylar at the upper end.

An egg of the Cabbage White on the underside of a leaflet.

A close-up view of an egg of the Cabbage White.

The egg takes about 3 days to hatch. The newly hatched has a length of about 1.8mm and a pale yellowish head capsule. Its cylindrically-shaped body is in a stronger shade of yellow and featuring sub-dorsal, dorso-lateral and lateral rows of small tubercles running lengthwise. Each tubercle has a moderately long setae emerging from the middle of it. The end of each setae bears a tiny droplet.

A newly hatched caterpillar of the Cabbage White eating its egg shell.

The newly hatched eats the empty egg shell for its first meal, and then moves on to eat the leaf lamina. Its body takes on a strong green undertone with the intake of leaf diet. In 2.5 days, the caterpillar grows to a length of about 3mm before the moult to the 2nd instar.

Two views of a 1st instar caterpillar, length: 2mm.

The 2nd instar caterpillar is yellowish green in body color with similar droplet-bearing setae as in the 1st instar. In addition, there are numerous small, black, conical tubercles dotting the body surface. Each of tubercles has a short black setae emerging from it. This instar lasts about 1.5 to 2 days with the body length reaching about 5.5mm.

Two view of a 2nd instar caterpillar, length: 4.75mm

Two view of a late 2nd instar caterpillar, dormant prior to its moult, length: 5.2mm

The 3rd instar caterpillar resembles the 2nd instar caterpillar closely except for the appearance of a faint yellowish dorsal band and a spiracular series of small yellow markings. The head capsule is now yellowish green. This instar takes about 2 days to complete with body length reaching about 9mm.

Two views of an early 3rd instar caterpillar, length; 5.8mm.

Two views of a 3rd instar caterpillar, length: 8.9mm.

Two views of a late 3rd instar caterpillar, dormant prior to its moult, length: 9mm.

Again, the 4th instar retains all the features as the 3rd instar. In addition, numerous fine and white setae, in greater proportion than in early instars, now adorn the body surface. This penultimate instar lasts about 2 days with body length reaching about 15.5mm.

Two views of an early 4th instar caterpillar, length: 10mm.

Two views of a 4th instar caterpillar, length: 15.2mm.

Two views of a late 4th instar caterpillar, late in thie stage, length: 14mm.

The 5th and final instar caterpillar resembles the 4th instar caterpillar closely. Its yellow dorsal band is more prominent than in the 4th instar. The many black tubercles dotting the bluish green body surface gives its a distinctive speckled appearance. The 5th instar lasts for 2.5-3 days, and the body length reaches up to 25mm.

Two views of an early 5th instar caterpillar, length: 14.8mm.

Two views of a 5th instar caterpillar, length: 25mm.

A pair of 5th instar caterpillars sharing a young stem.

Close-up, frontal view of the head of a 5th instar caterpillar.

On the last day of the 5th instar, the caterpillar ceases feeding and its body gradually shortens. It wanders around and comes to rest on the underside of a stem/stalk or a leaf of the host plant or adjacent plants. Here the caterpillar spins a silk pad and a silk girdle to secure itself and then becomes immobile in a head-up pre-pupatory pose.

A pre-pupatory larva of the Cabbage White.

Pupation takes place about 0.5 day later. The greenish, black-speckled pupa secures itself with the same silk girdle as in the pre-pupal stage, but with cremaster replacing claspers in attaching the posterior end to the silk pad on the stem/leaf surface. It sports a yellowish, thoracic dorsal ridge which is sharply raised at thoracic segment 2. This ridge ends in a pointed, yellow-tipped cephalic horn at the anterior end. The abdominal segments 2-4 are produced laterally into a black pointed tooth at each side of the abdominal segment 2. The dorsum is whitish on the anterior side of this transverse edge. In addition, two lateral whitish ridge lines run lengthwise along the entire length of the body. Length of pupae: 17-19mm.

Two views of the pupa of a Cabbage White.

Two maturing pupae of the Cabbage White.
Top panel features a male pupa and the bottom panel a female pupa.

After about 6 days of development, the pupal skin turns translucent as the development within the pupal case comes to an end. The markings on the forewing upperside become discernible and indicative of the gender of the soon-to-emerge adult. The following day, the adult butterfly emerges from the pupal case.

A newly eclosed male Cabbage White.

References:

• [C&P4] The Butterflies of The Malay Peninsula, A.S. Corbet and H.M. Pendlebury, 4th Edition, Malayan Nature Society, 1992.
• A Field Guide to the Butterflies of Singapore, Khew S.K., Ink On Paper Communications, 2nd Edition, 2015.

Text by Horace Tan, Photos by Bobby Mun, Mark Wong, Tan Ben Jin, Federick Ho, Khew SK and Horace Tan

Sexual Dimorphism : Part 1

Sexual Dimorphism in Butterflies : Part 1

Featuring Male-Female Differences


A mating pair of Orange Emigrant.  Left : Male, Right : Female

Sexual dimorphism in butterflies is the condition where the two sexes of the same species exhibit different characteristics beyond the differences in their sexual organs. These differences may include size, colour, distinguishing markings and secondary characteristics. In some cases the flight characteristics between the males and females are also distinctly different. The differences in sexual dimorphism can range from negligible to exaggerated, and may be subjected to sexual selection.

The degree of differences in sexual dimorphism in butterflies can be classified under a range that falls between negligible to exaggerated. I have further broadly categorised the differences into the following 4 categories :

1) Negligible : Males and Females appear so similar that it takes a bit more effort to scrutinise secondary characteristics closely to ascertain and differentiate between the males and females.

2) Subtle : Males and Females appear similar but there are minor giveaways that can instantly distinguish between the males and females

3) Distinct : There are clear differences between males and females that a glance will be able to separate between the two sexes in these species.

4) Exaggerated : The males and females of these species of butterflies appear so different that one could even assume that they are two different species.

A mating pair of Dark Brand Bush Brown.  Left : Female, Right : Male

These categorisations are by no means scientifically based and not intended as formal scientific classifications. As in any general layman categorisations, they are based on personal observations and there are certainly outliers and exceptions that may or may not fall clearly into any of these categories.

A mating pair of Pale Mottle

Then there are examples of dorsal and/or ventral sexual dimorphism. This is where the differences between males and females of a species are either on the dorsal (upperside) or ventral (underside) of the wings. In some cases, the differences are both on the dorsal and ventral sides of the wings.

A mating pair of two different morphs of the Lemon Emigrant

In some exceptional species, the sexual dimorphism is further expanded to polymorphism (i.e. more than just one form in either sex). This phenomenon may occur in just the females that display many different forms, or just the males that display many different forms. And then in some extreme examples, both the males and females display polymorphism. But by and large, only a handful of species fall into these categories. In Singapore, some examples are the Great Mormon, Malay Baron and Lemon Emigrant.

1 . Sexual Dimorphism (Negligible differences)

A pair of Lime Butterfly.  With a close look at the abdominal tips of the two individuals, it can be ascertained that the female is the top butterfly and the male is at the bottom

We now take a look at some of the examples of butterflies that fall into the 4 broad categories of sexual dimorphism. The first category is the most straightforward - where the males and females of a butterfly species are physically similar and it may take careful scrutiny to establish between a male and female of the butterfly. Examples shown here are certainly not exhaustive but just to illustrate some species that fall into this category.

Top : Male Lime Butterfly Bottom : Female Lime Butterfly. Note the size of the tornal spot and proportion of the blue-edged black spot to the red spot

Our first examples from the Papilionidae family would be the Lime Butterfly (Papilio demoleus malayanus). Ventrally (or seen from the underside), this species' sexual dimorphism can be considered 'negligible'. On the dorsal (upperside) of the wings however, the dimorphism may be considered 'subtle' as the main difference between the male and female of this species is the tornal spot on the hindwing. In space 1b on the hindwing, there is a red spot in both sexes. In the male, this spot is capped with a narrow blue lunule with a very narrow intervening black gap. In contrast, the red spot and the blue lunule in the female have a rather large black spot between them.

A mating pair of Psyche.  Difficult to separate between male and female from the underside

An example from the family Pieridae would be the Psyche (Leptosia nina malayana), in which the male and female are virtually indistiguishable when viewed from both the upperside and underside of the wings. The mottled underside and the predominantly white upperside with a black apical patch and a black spot on the forewing is almost identical in both the male and female of this species. This makes it near impossible to separate between the male and female of this species unless the primary sexual organs are examined.

From the Nymphalidae family, a good example of negligible difference in sexual dimorphism would be the Peacock Pansy (Junonia almana javana). This pair of mating Peacock Pansy demonstrates that there is almost little or no perceptible dimorphism between the male and female of this species. When viewed ventrally, it is difficult to separate the two. The two sexes are also near identical on the upperside with the usual ocelli present in both the male and female.

This pair of Common Caerulean (Jamides celeno aelianus) represents an example of negligible difference category as far as sexual dimorphism is concerned. Ventrally, the male and female is difficult to set apart from just the physical markings on the underside of the species. However, on the dorsal side, the sexes can be distinguished by the broader black border on the forewings of the female, making this species a dorsally distinct category.

Mating pairs of Skippers showing very indistinct differences between the males and females

Amongst the skippers, there is less sexual dimorphism in quite a number of the species in the family Hesperiidae. Quite a large number of the species can be classified under the negligible difference category. Examples shown here are the Large Snow Flat (from the sub-family Pyrginae), the Chestnut Bob and Grass Demon (from the sub-family Hesperiinae).

2. Sexual Dimorphism (Subtle differences)

Mating pair of Tailed Jay.  Female is the one on top, with its comparatively longer tail

The next category would be butterflies that demonstrate subtle differences in males and females of a species. The degree to which we can consider the "subtleness" in the difference between a male and female of butterflies is rather subjective, and here, we just give examples where there are minor features that are able to give away the difference between the sexes.

Left : Male Tailed Jay and Right : Female Tailed Jay.  Note the comparative length of the tails

A Papilionidae example of subtle difference between the male and female of the species is probably the Tailed Jay (Graphium agamemnon agamemnon). In this species, the key difference between the sexes is the relative length of the tail of the butterfly. Whilst the colour, spots and size are usually similar (with the male typically slightly smaller), the individual with the longer tail (usually twice as long) is the female. This very subtle difference separates the male from the female of this species.

Mating pair of Orange Emigrant.  The female, on the right, has darker and more pronounced spots on the wings

A typical example of a Pieridae that displays subtle differences between the male and female would be the Orange Emigrant (Catopsilia scylla cornelia). In the photograph shown of a mating pair, the female has more spots on the hindwings compared to the male, and on the dorsal side, the female has a black marginal border on the hindwing (absent in the male).

Mating pair of Plain Tiger.  The male, on the top, has an extra spot on the hindwing

From the subfamily Danainae, the secondary sexual characteristics of a sex brand on the hindwings is a subtle diagnostic feature that separates the male from the female. In the case of this mating pair of Plain Tigers (Danaus chrysippus chrysippus), the male (top) has an additional "spot" in the form of a sex brand on the hindwing. The female does not have this brand. This subtle spot separates the sexes in this species.

Mating pair of Apefly.  The female, on the left, has a more rounded forewing compared to the sharper and more angular shape of the male's forewing.

In this pair of Apefly (Spalgis epius epius), the structure of the wings is a very subtle giveaway in separating the male and female butterflies. The forewing of the male is more pointed and pronounced compared to the more rounded forewing of the (usually) larger female. The male, on the right of this photo, displays the more angular forewing and is obvious enough to distinguish between the sexes.

A mating pair of Common Mormon with clearly distinct features between the male and female.  These two categories will be discussed in Part 2 of this article next week.

In Part 2 of this article, we take a look at species with more distinct physical appearances between the males and females. We also look at the evolution of some of these examples of sexual dimorphism and ask some questions with regard to some of the reasons behind some of these evolutionary adaptations, probably by natural selection.

Text by Khew SK : Photos by Chng CK, Antonio Giudici, Khew SK, Koh CH, Loh MY, Tan BJ and Anthony Wong