Aposematism in Butterflies

Aposematism in Butterflies
The Theory of Warning Colouration in Butterflies

In an earlier article on Butterfly Predators, we saw how a butterfly's life is fraught with danger all around them, particularly from carnivorous predators. These range from birds and lizards, to spiders and dragonflies.

In 1866, Alfred Russel Wallace, in response to Charles Darwin, was the first to suggest that conspicuous colour schemes of some insects may have evolved through natural selection as a warning to predators. Following that meeting of the Entomological Society of London, John Jenner Weir conducted experiments with caterpillars and birds in his aviary for two years. The results he reported subsequently in 1869 provided the first experimental evidence for warning colouration in animals.

Aposematism is a secondary defence mechanism that warns potential predators of the existence of another primary defensive mechanism. In the butterfly world, the primary means of defence is usually because of the unpalatability of the butterfly.

The species that exhibit this primary defensive trait are usually those whose caterpillars have evolved mechanisms to sequester plant toxins and use them for their own defense. The butterfly species that have been able to synthesize these toxins at their caterpillar stages will present themselves as an unattractive prey to predators like birds and lizards, which may suffer diarrhoea or nausea after eating the butterfly.

Predators will quickly learn to avoid these species of butterflies, and very often, these are the species that exhibit warning colouration or possess easily recognisable and distinctive patterns on their wings. Once a predator 'learns' from experience that these conspicuous butterflies are distasteful, they will henceforth continue to avoid any similar looking (patterned or coloured) butterfles in future.

Amongst butterflies, the typical warning colours are black, yellow, red and orange. However there are others that are greys or whites, and not necessarily brightly coloured, but with patterns that are distinctive and prominent such that they become easily recognisable. These species tend to call attention to themselves, and are those that we human beings are also able to spot easily due to their "advertising" their presence in the field.

It is the colours, the combination of colours and the patterns that these butterfly species evolve, that make them recognisable to their predators. Aposematic colouration as a function of clarity - increased chromatic contrast, luminance contrast, and sharpness make a pattern easier to recognise.

Amongst the butterfly families, the species that display aposematic colouration are usually from the Papilionidae (typically feeders of Aristolochia spp), Pieridae (from the genus Delias), sub-family Danainae (almost all the species that feed on lactiferous vines such as Asclepias) and sub-family Heliconiinae (whose caterpillars feed on Passifloraceae).

However, it would be untrue to say that all brightly colourful butterflies are unpalatable. Other than those which mimic the unpalatable model, which will be the subject of a forthcoming blog article, there are other species that are as equally colourful and bright, but without possessing any primary defense characteristics and are hence fair prey for a predator.

So the next time you see a colourful and recognisable butterfly fluttering amongst the flowers in your garden, consider the fact that it may be intentionally attracting attention to itself as an advertisement of its unprofitability as a prey item to potential predators. To us humans however, we look in awe and admiration at its beauty and colours as one of Mother Nature's Flying Jewels.



Text by Khew SK : Photos by Henry Koh, Khew SK & Anthony Wong

I Spy, With My Little Eye

I Spy, With My Little Eye...

A Closer Look At The Eye of a Butterfly

In my childhood days, I used to play this game, "I Spy, With My Little Eye... something starting with the letter ..." on long car journeys that my family used to take down peninsula Malaysia, starting from my hometown in Penang, and reaching Johor Bahru and Singapore. It's just a little game of observation and quizzes to pass the time on the long trip down south.

The eye is a powerful organ in the animal world. It allows us to see and understand, recognise and react to the world around us. It is no different amongst invertebrates like butterflies. Unlike vertebrates, which are equipped with the single-lens eye, most invertebrates - crustaceans and insects - have compound eyes.



A compound eye is made up of many separate units called ommatidia (singular: ommatidium). Each unit has its own surface area, lens, and optic nerve fiber. It receives light from a small part of the animals field of view. The animal's brain integrates these views into a single image. Compound eyes are made up of many divisions, giving the eye a net or mesh like appearance. It is this multitude of divisions that gives it the name: Compound Eye.

Image courtesy of BioMEDIA ASSOCIATES

An insect's compound eyes usually bulge out and have a wide field of view. The lenses in compound eyes can't change focus, so insects can't see things that are far away. However, most things that concern an insect are up close and personal. The compound eye is very good at seeing things nearby and detecting motion.

Butterflies rely on colour to find food from flowers, and they have colour vision that is more enhanced than our own. A butterfly's vision is quite sharp at close quarters, but because acuity depends on the number of facets aimed at the object, butterflies are very near-sighted. Their colour vision has been experimentally proven, and in addition to all the wavelengths that we humans can see, butterflies can see far into the ultraviolet (UV) as well as infrared (IR).They use ultraviolet (UV) light to perceive patterns on nectar-laden flowers that are invisible to us, and they perceive the colours of flowers differently from human beings.

Recent research also suggests that colour sensitivity varies across different groups and species, and eventually this may offer some explanation for the behavioural differences observed between species.

Over many years of photographing butterflies, I have observed that the eyes of butterflies across different families and genera are rather distinctive. The shots below are a collation of the butterflies of different families.

Firstly for the Papilionidae, most, if not all, of the species have opaque jet-black eyes. The eyes are large and are totally black and featureless.

The next family, Pieridae, tend to have eyes that are more typical of compound eyes, with checker-board patterns in the eyes. The colour of the eyes is usually similar to the colour of the butterflies' general colour - typically whites or yellows.

The next family, Nymphalidae, is rather varied, having a total of nine sub-families of rather distinctive characteristics within the sub-families. The group shown below shows a combination of Satyrinae and Morphinae. The Satyrinae have striped compound eye structure, giving their predominantly grey eyes a banded appearance. The Morphinae are more varied, but one genus, Faunis, has a nice deep jade-green eyes.

The next subfamilies, Danainae, Heliconiinae and Apaturinae, shown below, have striped and chequered appearance. but some with rather vivid colours of yellows and greens.

The remaining Nymphalidae, featuring the families of Nymphalinae, Cyrestinae, Charaxinae, Limetidinidae, also show a variety of chequer-board and spotted appearances, and in many cases, where a larger distinct spot is displayed in some species. The Neptis also have a bluish-green sheen in their compound eyes.

Several species of the family Riodinidae feature emerald green eyes, whilst others have reddish brown eyes. Also, the sub-family Miletinae, which also sport striped compound eyes, have yellow-green eyes which appear almost iridescent in the field.

The Lycaenidae, which form one of the largest families of butterflies feature a whole spectrum of compound eye types, ranging from large hairy jet-black eyes, to spotted green and yellow eyes to metallic dark green eyes. My favourite is the deep green of the Arhopalas that make the eyes look like metallic jewels

The final family, the Hesperiidae, or Skippers feature extra large eyes, probably needed due to the butterflies' crepuscular (or flying in the early hours of dawn and the late hours during dusk) habits. Probably needing more light when flying at tremendous speeds during hours of low light, the Hesperiidae have, by far, the largest eyes amongst all the butterfly families. Several species feature scarlet or dark red eyes, with a darker centre within the compound eye. But most Skippers have dark brown and cleanly spherical eyes set in a rather large head of the majority of the Hesperiiidae.

So there you have it - even the eyes of our flying jewels are so varied and beautiful when we view them up close and personal to admire Mother Nature's works of art.

Text by Khew SK ; Photos by Khew SK & Horace Tan

References and Acknowledgments :

• The Butterflies of the Malay Peninsula, A.S. Corbet & H.M. Pendlebury, 4th Edition, The Malayan Nature Society
• Handbook for Butterfly Watchers, Robert Michael Pyle, 1984, Houghton Mifflin Co, Boston/New York
• Butterflies, Dick Vane-Wright, 2003, Natural History Museum, London
• BioMEDIA ASSOCIATES

Life History of the Common Awl

Life History of the Common Awl (Hasora badra badra)



Butterfly Biodata:
Genus: Hasora Moore, 1881
Species: badra Moore, 1858
Subspecies: badra Moore, 1858
Wingspan of Adult Butterfly: 47mm
Caterpillar Host Plants: Derris trifoliata (Leguminosae, Papilionoideae),
D. elliptica and two others (suspected to be Derris species).


A female Common Awl on the leaf surface of the Coconut Palm.

Physical Description of Adult Butterfly:

Adults are rather large in size with pointed forewing apex and markedly lobate hindwings. Above, the wings are dark brown. In the male, the wings are typically unmarked or with faint subapical spots. In contrast, the female has three pale yellowish subapical spots, large pale yellow hyaline spots in the cells and in spaces 2 and 3 on the forewing Wings bases of the female are ochreous. Below, both sexes are brown and often washed with purple, more so in pristine specimens. The forewing is pale yellowish to whitish at dorsum entering middle of space 2. On the hindwing, there is a small white roundish spot in the cell and an elongated white spot in the subtornal area. The spots on the forewing upperside correspond to those on the underside.

A female Common Awl with partially opened wings, showing us the various spots on its forewings

Field Observations of Butterfly Behaviour:

Adults are rarely seen in Singapore, likely due to its crepuscular nature. In contrast, the larval stages are rather readily found on various Derris species at multiple locations in Singapore. The adults are usually sighted in the vicinity of its larval food plants, typically ovipositing females. The usual perching site is on the underside of a leaf or other plant parts, resulting in photographs of "upside-down" adults being the most common takes of this species.

A male Common Awl on the underside of a leaf.


A male Common Awl pertching on the underside of a leaf.

Early Stages:

The 1st local host plant, Derris trifoliata, is a scandent shrub with 3-5 leaflets in a pinna, pink flowers, thin and flat pods. This plant is commonly found on coastal areas such as the Sungei Buloh Wetland Reserve and Kranji Nature Reserve.

Host plants : Derris trifoliata.

The 2nd host plant, Derris elliptica, is also a scandent shrub but with 9-15 obovate-oblong leaflets in a pinna and has brown pubescent branches. Extracts from both Derris species have been used as insecticides and by locals as "poison" for catching fish/shrimps.

Host plant : Derris elliptica.

Two other host plants, found in the nature reserves and in the Southern Ridges, are also woody climbers with 5-foliate and 7-foliate leaves. It is likely that they are Derris species too. The variegated early stages of the Common Awl feed on the young and still tender leaves of the host plants. The newly hatched and the 1st and 2nd instars typically feed on the youngest and still yellow/brown leaflets. Common Awl caterpillars of all instars also construct leaf shelters by joining leaf blades with silk threads.

Local host plants : unknown sp. #1 (left); unknown sp. #2 (right).


A mother Common Awl ovipositing on young shoots of Derris elliptica.

The eggs are laid singly on young shoots of the host plants. Each egg is white with a biege tinge. It is shaped like a pressed bun with a large flattened base (diameter: 0.9mm) and prominent ridges running from the pole to the base. The micropylar sits atop at the pole.

Two views of an egg of the Common Awl.


Mature egg (left), empty egg shell (right)

It takes 2-3 days for the collected egg to hatch. The young caterpillar eats just enough of the shell to emerge, and has a length of about 2mm. It has the typical cylindrical shape for skipper caterpillars, and the pale yellowish brown body has a number of moderately long setae. The large head is black, slightly bi-lobed and lightly hairy.

1st instar caterpillars. Top: early in this stage, length: 1.9mm.
Bottom: later in this stage, length :2.5mm.

The young caterpillar constructs its first leaf shelter by bringing two halves of a small young leaf together with silk threads. It rests within the flap and ventures out to eat on nearby leaf surface. In later instars, the Common Awl caterpillars also construct leaf shelters in a similar fashion but do so with larger and older leaves.

Leaf shelters and eggs found on young shoots and leaflets of unknown host #1.

After 2 days in 1st instar and reaching a length of about 4mm, the caterpillar moults to the next instar. The 2nd instar caterpillar has four faint yellowish dorsal bands, and a large number of faint yellowish rings on the body segments. Black dorso-lateral patches are found on the 3rd thoracic segment, 2nd, 4th, 6th and 8th abdominal segments.These patches increase in size as the caterpillar grows in this instar. All three thoracic segments are much smaller (narrower) compared to the abdominal segments, with the prothoracic segment being dark brown to black. The body and the head capsule are also covered in short fine setae.

2nd instar caterpillars. Top: early in this stage, length: 4mm.
Bottom: late in this stage,length: 8.5mm.

The 2nd instar caterpillar reaches a length of about 9mm, and after 2 days in this stage, it moults again. The 3rd instar caterpillar resembles the 2nd instar caterpillar but with more striking yellow coloration on the segmental rings and dorsal bands. This instar lasts another 2 days with the length reaching 14-15mm.

3rd instar caterpillars. Top: early in this stage, length: 9mm.
Bottom: late in this stage,length: 13.5mm.

The 4th instar caterpillar resembles the 3rd instar caterpillar closely. One noticeable change is the appearance of a pair of narrow black dorso-lateral patches on the 2nd thoracic segment. This stage takes about 6-9 days to complete with the body length reaching 25-29mm.

4th instar caterpillars. Top: early in this stage, length: 14mm.
Bottom: late in this stage, length: 25mm.

The final and 5th instar caterpillar has similar body markings and coloration as the 4th instar caterpillar. One unmistaken change is in the head capsule which has now become dark cherry red with three medium-sized black spots. The prothoracic segment is colored as per the head capsule and has a pair of black dorso-lateral stripes. Dense white setae cover the whole body. This stage takes about 6-9 days to complete with body length reaching about 41mm.

5th (final) instar caterpillars of the Common Awl. Lengths: 33mm (top); 36mm (bottom).


A close-up view of the head capsule of the final instar larva of the Common Awl.

Towards the end of 5th instar, the body of the caterpillar gradually shrinks in length. It ceases feeding and stations itself in its leaf shelter and enters the preparatory pupa phase. During the early part of this stage, the caterpillar spins large quantity of silk threads to seal the pupation shelter, and in particular, constructs a silk girdle at its 2nd/3rd abdominal segment and a short transverse silk band near its posterior end. Both the dorsal point of the girdle and the transverse band are also secured by vertical/oblique threads to the inner wall of the shelter.

Two views of a pre-pupa of the Common Awl.

After about 1 day of the pre-pupal phase, pupation takes place within the pupation shelter. The pupa secures itself with its cremaster attached to the transverse band. The pupa has a short thorax, a rather long abdomen and a black and pointed rostrum. Fresh after the pupation event, the body is pale yellow with large and cherry red spots (corresponding to the black patches on the larval body), but these fade 0.5 to 1 day later, and the body surface becomes mostly covered in a white substance. Length of pupae: 24-26mm.

Two views of a newly formed pupa. Note the red spots which will fade away within a day.


Two views of a pupa of the Common Awl with a coating of whitish powdery substance.


Sequence of three shots of the silk girdle from the pre-pupal to the pupal stage.
Note the girdle is suspended vertically with another silk thread to the shelter wall (or ceiling).


Three views of the posterior end from the pre-pupal to the pupal stage.
Note the transverse silk band and cremastral attachment to it during the pupal stage.


Two views of the cremastral attachment to the bundle of transverse silk strands.
Note the cluster of brown to dark brown hooks protruding from the cremaster to engage the silk threads.

After 6-7 days, the pupa becomes darkened in color signaling the imminent emergence of the adult. The next day the adult butterfly emerges from the mature pupa.

Two views of a mature pupa of the Common Awl



A newly eclosed Common Awl drying its wings near its pupal case.


A newly eclosed female Common Awl.

References:

• 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
• The Butterflies of Hong Kong, M. Bascombe, G. Johnston, F. Bascombe, Princeton University Pres 1999

Text by Horace Tan, Photos by Khew SK and Horace Tan.