Thirteen days have passed since the Mormon caterpillar cast off its larval skin, to be encased in its horny pupal case. The leaf-green pupa has darkened, showing colors of the scaly-winged insect counting down its emergence. I wait with my camera set and pre-focused. My flash-gun is ready, occasionally emitting impatient beeps. Just then, the pupa moves a little sideways, and a slit across the top widens to reveal the dark occupant. Slowly, the Mormon climbs out and hangs on the underside of the branch. Its shriveled, limp wings open out to expand slowly, as blood rushes through the hollow veins. It remains still, holding its wings slightly apart, waiting for them to harden. As the sun climbs into the sky, the Mormon flaps its wings for the first time.
This conjuring trick has been performed ever since butterflies first appeared on the planet. Around 300 million years ago, there seemed to have been a great insect `boom' in the lush, gloomy fern forests of the world. (Butterflies arrived much later, along with the evolution of flowering plants, and their association seems mutual). Though much of the evolutionary history of this insect is left to conjecture, the very few fossil records that have been found, show that the structure and pattern of the wing veins of the butterflies of around 30 million years ago appear very similar to those existing today.
The common Mormon is a swallowtail butterfly, so-called because most butterflies of this group (Papilionidae) have tailed hind wings. Swallowtails range from the world's largest birdwing butterflies to the delicate, almost translucent Apollos of the Himalayas and Alps. They can be classed into three main types; true swallowtails, to which the Mormon belongs, kite swallowtails, like the spot sword-tail or blue bottle, which have narrow, pointed hind wings resembling paper kites, and the third, the poison-eaters, so-called because their caterpillars feed on poisonous Aristolochia creepers, making subsequent adults a `protected species'. Some swallowtails, especially the iridescent birdwings of the South-East Asian rainforests, are known for their beauty and are coveted by butterfly-collectors around the world. Today, some 14 percent of the world's swallowtail species is threatened mainly due to habitat destruction and also from over-collection. About 80 species of swallowtails are found on the Indian subcontinent; India is one of the ten countries that have a fair number of swallowtails, out of the world's 700.
Of the many strategies evolved by nature for the survival of butterflies, adaptive coloration plays a major role. In other words, deception enables these insects to hide from enemies thus increasing their chances of survival and procreation.
One hot October noon, I chanced upon a female mormon sailing leisurely from plant to plant, drumming her sensitive legs on the leaves of every plant she came across. She eventually hovered a while over the tender shoots of a wild lemon tree, curled her abdomen, and laid a single, pale-green, sticky egg on the edge of a leaf (fluttering all the time). In all probability she returned, on subsequent visits, to add more eggs to this spot. She chose different plant shoots for her next batch of eggs, however, probably to ensure less competition amongst the newborn caterpillars, and also to make sure that all her eggs were not laid in one basket!
While the October sun still shone, the Mormon's eggs turned slightly orange and later transparent, to reveal the waiting caterpillar inside. And a week after the egg was laid, a tiny caterpillar ate its way out, making the eggshell its first meal. Just as egg-yolk provides nourishment to avian and reptilian hatchlings, so does the eggshell to butterfly larvae. The tiny, spiky caterpillar that emerged kept a low profile until it grew a little and began to resemble fresh bird droppings! Now it would lie all day long, conspicuous, but motionless, on an exposed part of the leaf, confining its feeding to the late evenings. This stage is the most vulnerable of all stages in a caterpillar's life since the little creature has neither wings to fly nor strong limbs to flee from birds, lizards, frogs, spiders, and wasps. Ichneumon wasps possess specialized needle-like, egg-laying tubes that can pierce the caterpillar's body for eggs to be laid inside. On hatching, the grubs slowly eat the caterpillar's innards, while carefully avoiding the vital parts, in order to keep the caterpillar alive. The grubs soon pupate and emerge to leave a dead hollowed-out caterpillar! Mason wasps carry away anesthetized (by the sting) caterpillars to store living food for their hatchlings. Therefore, the bird-dropping-like appearance of caterpillars, coupled with a frozen inanimate stance, successfully deceives many predators like birds, lizards, and frogs, that usually respond to the movement and appearance of their prey. Sometimes, this disguise may fail, and to counter this the caterpillar has a forked, bright-orange retractable organ (osmeterium), situated behind the top of its head, which protrudes to look like a pair of horns when the creature is alarmed. Besides having a startling effect, the organ emits a pungent smell -- that of the concentrated essence of the plants on which the caterpillar feeds; and most of the Mormon's food-plants are highly aromatic!
Once, while observing caterpillars, I noticed that a jumping spider was also very interested in one of the little creatures. Before I could guess at the wily spider's deadly intention, it had pounced and sunk its fangs into the rear end of one caterpillar. The caterpillar, almost simultaneously, reared backward, towards the spider, and its two-pronged `horns' shot out from its head. Even I was able to get a whiff of that pungent smell! This maneuver threw off the spider, that dangled by its `lifeline' and landed on the branch below. Though the caterpillar had successfully withstood and repelled the spider's murderous attack, it was not before the attacker's paralyzing venom had been injected. The spider, probably sure of the potency of the venom, tugged with its forefoot, at its web and looked up as if to get a bearing on the situation. It then jumped up onto a branch above the caterpillar. The spider's intention to renew its attack soon became clear to me, and as I watched it prepared itself for another assault. The caterpillar was now spewing out a green liquid, as an additional repellent, and its forked osmeterium protruded every now and then. The crippling effect of the venom was now probably fast making, itself felt. This time, the spider attacked from a different angle, finding a firm grip on the caterpillar's lateral side. In an instant reflex, the caterpillar directed its osmeterium at the spider, but unfortunately, an overhanging twig prevented the caterpillar from curling further backward, to bring its osmeterium nearer the spider. Though it repeatedly pulled and curled back, the twig spelled the caterpillar's doom. So, the spider held on till the caterpillar went limp and was carried off to be sucked dry. I was left wondering whether the spider had intelligently engineered the attack, fully aware of the overhanging twig, or whether it had just been lucky!
In its caterpillar stage, the Mormon is a virtual eating-machine, gorging itself on large quantities of leaves and tender shoots. It grows rapidly, both in length and girth. Its outer skin, being unable to accommodate a fast-growing body, is cast-off to be replaced by a new, elastic one. This takes place five times before the caterpillar finally encloses itself in a pupal cell. One ecological advantage involved in the butterfly leading two separate lifestyles is that the larva and the butterfly never compete for the same food.
When the caterpillar shed its skin for the last time, it donned a new leaf-green garb. Another new feature was two eye-like markings, on either side of its front, that made it look like the head of a green vine-snake! This resemblance is probably used to advantage, to scare off birds, lizards, and frogs. A few days later, the caterpillar stopped eating and became very sluggish. That same evening, as it began to grow dark, the caterpillar became restless, feverishly creeping up and down the branches till it came to rest on the underside of a branch. Here, it spun a silk pad to attach its rear end, and a silk band supported its body from the branch. Thereafter, it remained immobile until the next evening when it started wriggling about, all the while remaining firmly attached to the branch. The larval skin split from the top of its head and was worked backward until, eventually, it was discarded. With the old skin went the mouthparts and legs that were now no longer needed.
A rapid process of cell division had begun within the pupal case, to create a new entity that bore not even the slightest resemblance to its previous `grubby' look. The caterpillar's pupa too is well camouflaged to look like a leaf. This pupal stage, though brief, undoubtedly seems to be the safest period in the Mormon's life. I noticed that a caterpillar, which pupated amongst dried twigs, did not sport the usual leaf-green color but was mottled brown and black, giving it a broken twig-like look, to render it almost invisible in its habitat. This instant adaptive coloration was intriguing, and it seems to work well since I was often not able to locate the pupa, though I could the caterpillar. Even in this quiescent mummified stage, when the pupa appears quite defenseless, it would make a snake-like hissing sound, by moving its rear segments. I was a bit taken aback when I first heard this as my fingers, one day, accidentally brushed against it. This audio-effect is certainly meant to scare off those predators that dread snakes!
Henry Walter Bates, an English naturalist first became aware of mimicry in nature in the 19th century. While working in the jungles of South America, he found that two different species of butterflies not only looked alike but were matched in their behavior as well. This phenomenon, today, is known as Batesian mimicry. The adult Mormon is a classic example of Batesian mimicry, where the female Mormon, because of her biological importance, exists in three different color forms. In one rather uncommon form, the female looks very much like the male, while in the second and third form, the female Mormon mimics two entirely different species of red-bodied, distasteful swallowtails (the crimson rose and the common rose). These red-bodied swallowtails, during their larval stage, feed on poisonous Aristolochia vines and thus retain the plants' poisonous essence, in the form of body poisons, in the adult stage. The presence of these body poisons is advertised by warning colors that generally take the form of red spots on the wings or body. The butterflies often fly slowly, to emphatically advertise their inedibility. They do not even attempt to escape when disturbed. A young, inexperienced bird, for instance, will attack and attempt to eat a conspicuously colored butterfly, but it soon becomes aware of its extremely unpleasant taste. The bird, subsequently, recalls its distasteful encounter with those colored butterflies and therefore will hesitate to attack another similar-looking one.
Mimicry is not a conscious effort on the part of creatures but is a process of the selection of favorable genes and the elimination of those unfit ones that might involve several generations before the imitation is perfected. At some point in time, a mutant individual is born with a color closer to a distasteful far-off related species. Hungry birds feeding on its brothers and sisters may overlook it. And so it lives on, to breed and pass on this trend of protective resemblance until, through a selective process over successive generations, the mimics refine themselves to such a point that they easily pass off for their models. On the other hand, those butterflies which turn out to be poor mimics are more likely to be predated upon. In this way, those individuals that are not confused by the model are `corrected' leaving only perfect copies. Traits that tend to give away the mimic are eliminated over a long period of time, through natural selection. For the success of this type of mimicry, it is essential that models occur in greater numbers, and in the same area, in order that predators encounter more of the real, distasteful models and thereby the association of warning-coloration with the actual unpleasant experience is deeply imprinted on the predator's mind. With every distasteful model attacked, the chances of the mimic's survival increase.
It is only the female Mormon that is blessed with the genetic ability to mimic the two red-bodied swallowtails, and she survives on the unpalatable reputation of these models. Not only is the color pattern of her wings perfectly copied, but even her flight pattern is similar --slow-sailing to allow predators to recognize her `assumed' warning colors. The only difference is that her body color is not red like the model. The male Mormon, which has no protective coloration, is a swift-flying insect and rarely rests, except perhaps to bask in the morning sun in order to warm up his cold-blooded body.
What amazes me most is that during the monsoon, when both the red-bodied swallowtails are abundant, I saw that the female Mormon occurred in both the corresponding forms. However, with the departure of the monsoon, when the crimson rose becomes scarce, the Mormon female mimicking it, also becomes less abundant and for the rest of the year, only the common rose is to be seen cruising along leisurely with its `copy'. An explanation to this may be that, normally, both male and female Mormons carry genes of all three forms, but those genes with false warning-coloration, being sex-controlled genes, find expression in the female body only - somewhat similar to color differences we see between the male and female of several other creatures. Among the two female forms, the crimson rose form gene, which is less dominant can be expressed only under certain climatic conditions, for instance during the monsoon.
Photo: Isaac Kehimkar.
As I watch a female Mormon hover over some lantana flowers and extend her coiled, straw-like tongue into the inner recesses of the blooms to avail of the energy-giving nectar, I wonder why only the Mormon female is shielded from predators, while the male is denied that genetic facility. Perhaps frequent attacks on the female, while she is carrying and laying her eggs, has led to this natural selection, in order to ensure a female fit enough to survive. Conversely, the male being a swift flier is never very vulnerable to predatory pressures and therefore the need for any special survival strategy does not arise.
As I continue to watch the female Mormon flitting from flower to flower, a male suddenly darts up and starts fluttering around her. The female loses interest in the flowers and the male now begins flying around her in tight, vertical circles. The couple slowly rises high amongst the mango leaves, to merge in with the dark canopy. The male must either have seen her or smelt her presence since female butterflies produce a sex attractant called pheromone - the gland responsible for this scent being situated at the tip of her abdomen. Males too produce pheromone from a small gland which is at the base of specialized scent scales on the hind wings, called androconia. This serves to act as an aphrodisiac of sorts. If the male succeeds in wooing a female, she will settle, and the male will grasp the end of her abdomen with his abdominal claspers. The pair will then remain together for an hour or so, and if disturbed, the male will carry her off to safety. A package containing sperms, called a spermatophore, is passed to the female that retains it until egg-laying. One mating session is enough for the female to produce 60 to 150 fertile eggs during her entire lifespan of a month.
Mormons belong to that group of butterflies (swallowtails) that inhabits the tropical regions of the world, where rich forests and other natural habitats are fast disappearing. Many swallowtails are, in fact, exclusively forest-dwellers. Butterflies, like other insects, are dominant components of the web of life. Being so diverse and ecologically important, they are the first to get affected by any disturbance to their habitat, even if it is only slight. Conspicuous insects like butterflies and dragonflies are, therefore, particularly valuable in monitoring ecological changes and serve to warn us of today's deteriorating environment.
The caterpillar stage is the most vulnerable of all stages in a butterfly's life. Since the little creature has neither wings to fly nor strong limbs to flee, it, therefore, defends itself by remaining exposed, but motionless, on leaves, when it hatches, resembling fresh bird droppings. No bird or lizard would ever consider eating droppings!
If this disguise fails, the insect counters attack with the help of a bright-orange pair of forked, `horn-like' organs called the osmeterium, that serves both to startle predators and also give off a strong, pungent smell -- that of the aromatic leaves it feeds on.
A third defense mechanism the caterpillar avails of is appearing large and dangerous. Here, the little green caterpillar resembles a green vine snake's head, complete with two prominent eye-like markings on either side of its head!
An adult male Mormon. Strangely, only the female Mormon is blessed with the genetic ability to imitate two red-bodied swallowtails; the male Mormon has no protective or warning coloration. While the female Mormon even flies slow enough to `advertise' her inedibility and allow predators to take note of her `assumed' warning colors, the male Mormon is a swift flier and rests only for brief moments, to bask in the warm sunshine.
Photo: Sunjoy Monga.
A Mormon usually emerges from its pupa within 13-15 days, unless unfavorable conditions delay it to a couple of months or more. The pupa stage is perhaps the safest period in the butterfly's life. Usually neatly camouflaged among leaves, and held to a branch by a silken band, it rests motionless, though even in this stage the pupa makes a hissing noise, by moving its rear segments when disturbed.
A slight split in the pupa reveals its dark occupant.
That slowly climbs out.
Photo: Isaac Kehimkar.
Clinging to its support.
Author: Isaac Kehimkar, Sanctuary Asia, Vol. VI No. 3, 1986.