The Study of Butterflies 4

SERIES I ARTICLE The Study of Butterflies 4. Defences and Defensive Behaviour Peter Smetacek In this part we look at some strategies adopted by butterflies Peter Smetacek works on that enable them to avoid predators. the taxonomy and zoo- geography of Indian Butterflies are a fine example of how creatures that are perfectly Lepidoptera. He is also interested in exploring non-aggressive can survive in nature. Indeed, they are not only the potential of Lepi- surviving, but are also thriving. These fragile-looking, shortIived doptera as bio-indicators creatures have been around for millions of years, much longer of ecological functions than humans, or even the genus Homo: 35 million year old and groundwater. butterfly fossils from Europe and North America all bear the distinguishing characters of modern-day butterfly families, so ancestral butterflies must have evolved much earlier than that. Port 1. The Naming of Indian But Butterflies are found almost everywhere that it is possible for a terflies, Resonance, Vo1.5, No.6,pp.8-14, 2000. creature to survive, from the harsh and cold Arctic tundra to hot Part 2. Flight, Fuels and Senses, deserts like the Thar and Sahara and, of course, in very large Resonance, Vo1.5, No.8, pp.4-12. numbers in equatorial rain forests. 2000. Port 3. Intra-specific Variation, No butterfly can bite, sting, cause an itch, squirt acid or spring Resonance, Vo1.6, No.5, pp.8-15. similar unpleasant surprises on would-be attackers. This is one 2001 . of the major reasons why they are among the most attractive insects to us. The other reasons are obviously their large size, wonderful colours, and graceful flight. One would expect that creatures other than humans would also find them attractive for the same reasons, but with a sinister rather than appreciative purpose in mind. If butterflies were entirely defenceless, they would probably be more or less extinct by now. In reality, they are thriving, so they must have a few dissuasive tricks up their sleeves, or rather on their wings. These tricks are mainly passive defences, of which butterflies have an impressive array and some of the better known ones are discussed in this article. Keywords Defence, flight. settling and The adult stage of butterflies differs from the early stages in that distastefulness; in butterflies. it is highly mobile. Due to this mobility, it has to face and outwit -8-------------------------------~---------------R-ES-O-N--A-N-C-E-I--M-a-Y-2-0-0-2 SERIES I ARTICLE not only actively foraging predators such as birds but also predators that lie in wait, such as praying mantises, web-spiders, flower spiders, frogs and toads. As a result, no butterfly restricts itself to a single line of defence. Flight Flight is the primary mode of progression of adult butterflies. As with other modes of progression, it is also the primary means of escape from dangerous situations. A large number of butter flies have mastered the intricacies of rapid flight and habitually zip about. Others have a rather moderate or even slow flight, but nearly all are capable of considerable bursts of speed over short distances if they feel the need to escape. Few can keep up the 'escape velocity' for long and generally slow down as soon as they feel themselves to be out of danger. The ability to fly fast requires the development of powerful flight muscles. These, in turn, require large amounts of energy to operate efficiently, besides turning the possessor into a spe cially dainty morsel, with more flesh than bones (sorry, chitin). The best examples of the followers of this model of passive defence are perhaps the Skippers (Hesperiidae), which are Lepi doptera intermediate between moths and butterflies. Almost all the 3000 species of Skippers found worldwide have a stout thorax housing powerful flight muscles (Figure 1) and habitually Figure 1. The broad thorax fly at such a speed that they are quite difficult to follow with the of this Skipper (Ce/aenor eye. They are very wary and rarely allow one to approach close. rhinus sp.) houses power The drawback of this otherwise very safe system is that the ful muscles that enable the minority of species that are active throughout the daytime need butterfly to fly very fast. to spend a great deal of their waking hours searching for and (Credit: Peter Smetacek) sucking up nectar to feed their powerful muscles. The majority of Skippers are active only for a few hours each day at dawn and dusk, when they zip about in the gloaming to locate mates. It is suspected that such species are also active at night (Box 1) but nothing is known about this for certain. Other groups that habitually fly fast are the Hairstreaks (Lycaenidae) and some Nymphs (Nymphalidae). Like the Skip- ________,AAflA~~ ______ __ RESONANCE I May 2002 v V VV V \r' 9 SERIES I ARTICLE pers, the Hairstreaks are rather small butterflies that fly so fast it Box I is difficult to follow them with the eye. They are active during It has been proposed that, the daytime and, like the diurnal Skippers, spend a good part of originally, there were no their time locating food and feeding. day-flying Lepidoptera. However, as bats per Among the Nymphs, the Rajahs (Charaxes spp.) and Nawabs fected their sonar-based (Polyura spp.) are notably swift fliers, with a broad thorax. They hunting system, pressure are capable of very fast flight but, because of their large size, they grew on the night-flying are comparatively easier to follow with the eye than Skippers Lepidoptera and some and Hairstreaks. Like these two groups, they require large species evolved to exploit quantities of food but prefer rotting fruif or crabs, animal the hours of daylight, droppings and other foul substances to flowers. when predator pressure is comparatively less. In The second division consists of those butterflies that fly rapidly support of this proposi but not as fast as the Skippers and the Rajahs and Nawabs. tion is the fact that, com Nevertheless, such butterflies are capable of short bursts of pared with moths, there speed that can match those of the Skippers. Most of the Swal are relatively few butter fly species. Nor does the lowtails (Papilionidae), Nymphs, Whites (Pieridae), Blues and diversity of physical Coppers (Lycaenidae) fit in this category. Their flight is moder structures found among ately swift and even a hint of danger is enough to cause a burst of butterflies match those speed that will leave most pursuers behind. found among moths, sug gesting moths are a more This is the middle path in the trade-off between powerful ancient group. Even to muscles and the ability to live off relatively scarce food re day, predator pressure is sources. While members of the 'second division' are avid feed much greater for night fly ers, they do not have as stout thoraxes as Skippers and Hair ing Lepidoptera, for streaks. They spend a good part of their waking hours flying and though birds fill the role most are capable of sustained flight, unlike the very fast fliers of predators. during the that tend to settle frequently. day, most birds capture resting butterflies and The third approach to safe flight is practised by the Tigers, there are very few species Crows, Costers, Windmills, Roses, some Browns and some Whites of birds worldwide that that habitually fly slowly and are capable of only moderate habitually capture flying butterflies, unlike bats bursts of speed even when threatened. While"the Tigers, Crows, which routinely predate Roses, Windmills and Costers deliberately fly slowly to adver upon flying insects. tise their distastefulness, the Browns and Whites depend on erratic flight to escape attacks (Figure 2). The hopping flight of some Browns, which proceeds in a series of bounds or nops, with -o-------------------------------~-------------------------------- 1 RESONANCE I May 2002 SERIES I ARTICLE the wings closed over the thorax in the upper half of the hop, enables them to move through dense vegetation where pursuit is impossible. Many Browns feed on grasses or bamboos and they are consequently commonest in areas where these plants grow. They are the only butterflies capable of getting through bamboo clumps undamaged and, when disturbed, will often fling them selves into the middle of a handy bush or bamboo clump where, if followed, they will display equal dexterity in making their way to the other side of the bush or clump, leaving the cause of Figure 2. Cabbage Whites disturbance struggling to get through! (Pieris spp.) have devel oped erratic flight to a fine The Whites, especially Cabbage Whites, species of which are art. (Credit: Rajani Smetacek) found throughout Europe, N Africa, N Asia, the Himalaya and the Nilgiri and Palni hills, have mastered the art of erratic flight. Seen from a distance, they appear to be progressing in a single direction, but the lurches, dips, hops and spurts that make up the flight of these creatures make it difficult to believe that the creature is not thoroughly intoxicated. Such flight, though ludicrous at one level, is a masterful feat at another, since it enables the butterfly to dispense with powerful muscles and the fuel required to power them, while permitting relatively safe passage through hostile territories. Certain species of birds, such as crows and seagulls, are known to Erratic flight, though enjoy utilising upcurrents of air, rising effortlessly with wings ludicrous at one outspread and diving down again from a height, to repeat the level, is a masterful process over and over again. At least two species of butterflies, feat at another, the common mime (Papilio elytia) and the BI ue Apollo (Parnassius since it enables the hardwickei) do more or less the same thing.

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