Why Study Butterflies?
WHY STUDY BUTTERFLIES?-Jesmond Harding
Many scientific reasons are advanced for the study of Lepidoptera. These include the significant role that butterflies and moths play in many of the world’s ecosystems – as herbivores and as food sources – and for the vital contribution they make as pollinators. Butterflies are also studied for their role as indicators of climate change, habitat quality and for their role in pest control. However, while these are important reasons for studying butterflies and moths, there are also lessons that butterfly behaviour can teach us, about success, about adapting to our environment and about how we need to change to ensure our own survival. It is these aspects I will explore in this article.
Our success in life very much depends on our behaviour and this is no less true of a butterfly. Humans as intelligent beings make decisions and select between options; butterflies act in certain ways when in certain situations too, but they do not make choices in ways that we do. Instead butterflies respond to stimuli and to environmental signals. While response to external stimuli can involve highly complex processes, such as the diapause syndrome, butterflies rely on sensors to receive and process the information to which they react more swiftly, not in a conscious but in an instinctive way.
Thus the insect has the necessary information to ensure its survival. This means that it reacts appropriately to gradual change and to more immediate threats to its survival. While a butterfly’s compound eye contains several thousand ommatidia, each one a functioning eye, it is unable to interpret patterns on another butterfly’s wing. However, it is highly sensitive to movement within its field of vision. When an object is moving swiftly towards it, a butterfly usually takes evasive action regardless of whether the object is a falling leaf or a predatory bird. This means that the butterfly does not require intelligence to avoid danger. It simply needs to react to stimuli in ways it is programmed to do, eliminating the need to make choices that are likely to take a fatal time period to formulate. In some circumstances humans do this too, when we rely on our instincts to swiftly avoid what we suspect, but do not certainly know, to be hazardous circumstances.
The fact that butterflies do not make decisions like us does not mean that features governing a butterfly’s response are uncomplicated. Take for example the emergence of the Orange-tip butterfly that overwinters in the pupal stage. It is important for the species and for an individual butterfly that it emerges when conditions favour its needs. Temperature is a stimulus that affects emergence but it cannot be the only factor; if it was, the butterfly might emerge too early and out of synchronisation with the development of nectar sources and of its larval host plants. Brown Hairstreak Thecla betulae larvae feed on the developing leaves of its larval host-plant Common Blackthorn Prunus spinosa. The leaves are only suitable for a short period of time and if the larva fails to hatch at the correct moment they will have insufficient food and die (De Vries et al., 2011).Therefore the sensors that detect seasonal changes must be interactive; the emergence time must be governed by multiple factors such as temperature, daylight levels (photoperiod) and possibly humidity levels. It appears that a species’ response to these factors varies depending on latitude. Typically a butterfly that is single-brooded in cooler conditions in a northerly location or at a higher altitude may produce two or more generations if living a warmer location further south at low altitude. In the south of England in a year with a warm spring and good summer with sunny weather extending into autumn the Common Blue Polyommatus icarus is capable of producing three generations. Warmth and daylight length/sunshine hours are thought to be the ecological influences on the number of generations the species can produce there. However larvae from Scotland, where the Common Blue produces only a single but more prolonged generation each year still only produces one generation when reared in the south of England – even though the summer daylight length in Scotland is longer than it is in the south of England. The univoltine (one generation) character of Scotland’s Common Blues appears to have a genetic basis, not one arising from ecological conditions. Is it the case, then, that the Common Blue in Scotland has adapted to its latitude by producing a subspecies hardwired to produce only one brood regardless of altered ecological circumstances? The range of circumstances that we must take account of in making important life choices can involve a complicated process of weighing the various consequences. Happily for the butterfly, its big decisions are pre-determined by its genetic character and response to signals from its environment. This does rely however, on change remaining predictable; some species may not be able to react quickly enough to rapidly changing circumstances.
This brings me to a closely related lesson we can learn, that of timing, this time from butterfly phenology. Phenology is the study of periodic life cycle events and how their timing is influenced by factors such as seasonal changes, interannual changes in climate, overall climate change, global warming and also habitat factors, such as those influenced by latitude and altitude. Phenology studies involving butterflies are popular at present as scientists plot first and final flight dates and the dates of peak emergence as well as the number of generations (voltinism) in order to track evidence for the impact of climate change. Scientists also examine, in tandem with butterfly phenology, the phenology of the larval host-plants. Yet in a philosophical sense we can gain a view, from observing butterflies, of the crucial importance of timing. In Shakespeare’s Julius Caesar, Brutus believed that choosing the right time was pivotal to attainment of success:
There is a tide in the affairs of men,
Which, taken at the flood, leads onto fortune;
Omitted, all the voyage of their life
Is bound in sorrows and in miseries.
On such a full sea are we now afloat,
And we must take the current when it serves,
Or lose our ventures. (Act 4, Sc 3 218-224)
The Bible tells us
There is a time for everything and a season for every activity under the heavens;
A time to be born and a time to die… (Ecclesiastes 3:2)
In many circumstances timing is crucial; Mark Anthony’s timely speech at Julius Caesar’s funeral turned the Roman crowd against Caesar’s murderers. In the early nineteenth century the world’s most powerful man, Napoleon, choose to fight the Russians in mid-winter, with disastrous consequences for his army. A butterfly must also get its timing right and to do so it is superbly kitted out with the programmes needed to “tell” the butterfly when to emerge, how many broods it can fit in during a particular season, when to breed or delay breeding, when to migrate and when to seek a safe haven in which to spend the coldest period of the year. The next time you see your first Orange-tip butterfly in spring I invite you to feel not just the euphoria of its beauty and confirmation that the season has changed but also the wonder of knowing that the butterfly has got its timing right. Furthermore its timing is not simply right “on the day.” Butterflies do not usually play the high risk “winner takes all” strategy with survival but instead play a “longer game.” Emergence for the Orange-tip occurs over a lengthy period in spring and summer to guard against a return to winter or a prolonged bad spell. (The flight period recorded on Butterfly Conservation Ireland’s Record page for 2015 is from April 7th to June 29th).There is evidence that not all pupae will hatch in one year, an extra precaution against unfavourable circumstances.
Success for us can also depend on our appearance, which influences our behaviour and other people’s perceptions of us. In order to prosper we strive to make the right impression and in this the way we dress is influential. We often trust people who look presentable. A suit is worn to a formal interview. Those charged with maintaining public order are uniformed. In both these examples dress lends itself to restrained, orderly conduct. A soldier in desert terrain wears sand coloured clothing that assists in concealing him from his enemies. Through our appearance and behaviour we interact in complex ways with our bosses, colleagues, rivals and our broader environment.
A butterfly has much to teach us about the relationship between appearance, behaviour and the nature of its environment. All is not always what it seems; it is easy to understand why the Green Hairstreak Callophrys rubi which spends much of its time perched on willow, birch and hawthorn has an emerald green underside but why does the Purple Hairstreak Neozephyrus quercus which spends most or all its life perching up high in oak trees possess a silver grey underside? On 1 August 2015 I scanned the top of the oak canopy in Crom Estate, Fermanagh as large dragonflies scoured the tree tops. Warblers and tits were also present. However, the Purple Hairstreak’s coloration must offer protective camouflage otherwise its genes would have been long extirpated. Aphid honeydew often coats the oak leaf surfaces and the hairstreaks feed on this – consequently they rarely need to fly to obtain their food. Instead they sit still for long periods, probing leaf surfaces for nourishment. The aphid secretions sharpen the silver glare glossy oak leaves show in bright sunlight and now the butterfly’s mimicry is revealed. Indeed, its coloration and sedentary behaviour combine to protect it from its predators; sharp-eyed though they are, dragonflies and birds often need to detect movement to locate prey. As for the role of timing, activity such as mate-seeking and battling between rival males is delayed until later in the afternoon often in the warmest part of the day when the butterfly has absorbed the heat it needs but when birds are less active. We also see complex interaction at play here between elements within the butterfly’s ecosystem.
Another survival strategy we share in common with butterfly and moth populations is migration. Since humans first walked the earth we have moved in search of resources. Recently we have witnessed a huge movement of people to the wealthier areas of the world, mainly from the southern to the northern hemisphere. Many migrants are more accurately termed “economic migrants” who move to seek a better life. The Red Admiral Vanessa atalanta, mainly reliant on the Stinging Nettle Urtica dioica for breeding, behaves similarly. With seasonal regularity, the butterfly moves north from its Southern European and North African base early in the year, arrives at suitable breeding grounds, and produces a new generation which in turn moves further north until, by August, through successive generations most of Europe is occupied. Meanwhile, in its southern haunts, the sun has scorched its larval host- plants rendering them unsuitable. In moving north the butterfly is following its food. When cooler conditions in northern areas begin to lead to declines in food plant availability and quality, the southern areas too begin to cool down and receive rain, making food available there once more, leading to reverse migration.
Why study butterflies? I believe that the greatest lessons we can learn is from the examples we are given. In learning to read the signals in its environment, when to take the next step in its life cycle, how to deal with the threats in its environment, the humble butterfly has ‘learned’ to take care of itself, by adapting to its world. Modifying our environment and man-made climate change is pushing the limits of some butterfly species. Some of the more vulnerable butterfly species may not be able to adapt and synchronise with their environment quickly enough. Furthermore, we need to ask whether we are adaptable. Or have we simply used our large brain to remodel the world to deliver what we want? We do not live in harmony with the rest of nature, in the way that butterflies do. Neither have we looked after the world. Instead we exploit the world to serve our desires.
Perhaps, in the end, our survival will depend on us learning that we are part of nature, not apart from it.
Butterflies are flagship species. They grip the public imagination and by researching and conserving them you not only save the butterfly but also the ecosystem. The next time you see a butterfly or moth, marvel at what it has learned, and learn to protect the world we share with him.
Butterfly Conservation Ireland (2015) 2015 records. Butterfly Conservation Ireland. Online at: http://www.butterflyconservation.ie/wordpress/?page_id=3842. Accessed 13 January 2016.
De Vries et al., (2011) Synchronisation of egg hatching of brown hairstreak (Thecla betulae) and budburst of blackthorn (Prunus spinosa) in a warmer future. Journal of Insect Conservation, Vol. 15, No. 1-2, 2011, p. 311-319.
Emmet, A.M. and Heath, J. (eds) (1990) The Butterflies of Great Britain and Ireland. 7 (2). Harley Books, Colchester.
Tolman,T. & Lewington, R. (2009) Collins Butterfly Guide. Collins, London.
Photographs ©J. Harding.
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