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1. INTRODUCTION
Butterflies and moths are
animals without a backbone (invertebrates), with jointed
legs (arthropods). They have six legs (insects) and scaled
wings (Lepidoptera). The Order Lepidoptera (moths and
butterflies) is divided into more than 30 superfamilies.
Three of these superfamilies, the Papilionoidea (true
butterflies), Hesperioidea (skippers), and Hedyloidea (a
small Central American superfamily) are regarded as
“butterflies” by most people, while all of the other
superfamilies are considered to be “moths”. | ||||||
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2.
DIVERSITY AND SPECIATION | ||||||
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3. LIFE CYCLE The life cycle of butterflies and moths is one of the most incredible phenomena of the natural world, and fascinated me as a child, leading to my life-long passion for these creatures. Each of the four stages of the life cycle is unique so that each species is, from an ecological perspective, actually four creatures rolled into one. The egg (ovum) is a small spheroid of about a millimetre in diameter that is deposited by the adult female, either singly or in batches, on or near the larval food source. Within it the embryo develops into a caterpillar (larva) in a week or so. The larva chews its way though the shell (chorion) of the egg and proceeds to feed at a prodigious rate. When it becomes too big for its skin (cuticle), a larger one forms below and the old one is shed. Usually there are five larval stages (instars) and four moults. The duration of the larval stage is variable but is generally completed in a few weeks. The final larval moult results in the formation of a pre-pupa, a soft unformed thing which wriggles and changes shape as it hardens into a chrysalis (pupa). Within hours the shape of the adult body, wings, eyes, and antennae becomes apparent below the cuticle of the pupa. The duration of the pupal stage is also variable but generally lasts between one and two weeks. A few days before the adult butterfly (imago) emerges the pupa “colours up” and the adult insect can be clearly seen below the pupal cuticle. On emerging the adult splits the pupal case along defined sutures and hangs, with crumpled wings, from the empty shell or crawls to a nearby support. Over the next hour or so the wings gradually expand and harden. This is achieved by pumping body fluids into the wing veins. Once the wings have hardened the butterfly is ready for its maiden flight, in search of food and a mate. Butterflies that occur in favourable (more or less non-seasonal) environments, such as tropical lowland forest, breed continuously, with as many as 10 generations a year. In harsher environments, particularly those with dry, or freezing periods and periodic fires the indigenous butterflies have only a few or a single annual generation. These species bridge these unfavourable periods by diapausing (‘hibernating’) in one of the life stages. Diapause in the egg stage is well documented in some butterfly species in the Northern Hemisphere but not in Afrotropical butterflies. Larval diapause is a common strategy in browns (Satyrinae) in grassland habitats and in Lycaenidae, especially those associated with ants (myrmecophiles). Pupal diapause is seen in swallowtails (Papilionidae), some swordtails (genus Graphium) sometimes remaining in the pupal stage for several years. Adult diapause is relatively rare in Afrotropical butterflies and is best exemplified by the nymphaline (Nymphalinae) genus Precis, which has dry-season form adults that look very different from the breeding summer forms. It is important, from a biological viewpoint, to realize that it is the larval stage that is of greatest ecological importance since it is the larva that is the prime ‘energy-gathering’ stage. There is no nutrient intake in the transforming egg and pupal stages, and largely only ‘maintenance’ energy intake by the adult (adult butterflies do not grow!). The adult stage should only be regarded as the dispersal and reproductive phase of the life cycle. |
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4. GENERAL ECOLOGY Some butterfly species have enormous geographic distributions while others are exceedingly localized. The painted lady (Vanessa cardui) occurs throughout Africa, large parts of Europe and America, Asia and even parts of Australia. At the other extreme, the Brenton blue (Orachrysops niobe) is found only in a locality about one hectare in size, near Knysna, in the Western Cape Province of South Africa. How can these discrepancies be explained? The main reason why the painted lady has such a wide distribution is because it is an extreme ecological generalist, while the Brenton blue is an extreme specialist. Painted lady larvae can feed on the leaves of hundreds of different plant species, the adults are great ‘migrators’ and ‘dispersers’, and the adults (and early stages) can tolerate extremes of temperature. The Brenton blue, on the other hand, breeds on a single plant species that has a very restricted geographical distribution. In addition, the larvae are associated with a specific species of Camponotus ant. Adult Brenton blues are ‘colony-bound’, seldom venturing beyond the limits of the colonial boundaries. Species with a wide distribution should, however, not automatically be regarded as ‘common’, nor those with restricted distributions as ‘rare’. Sometimes a species is widespread but rare, sometimes it is local but abundant! Adult butterflies can live for a few weeks to a few months but most die before they can become ‘old’, either falling prey to a predator, inclement weather, or some other accident (such as the radiator of a fast-moving vehicle). Tropical and subtropical species tend to have continuous overlapping broods so that adults and the early stages are present in more or less constant numbers throughout the year. At the other extreme are univoltine species, with only one brood a year. Species with a single annual brood predominate in seasonal habitats having long dry spells or cold winters. Depending on the species, the eggs, larvae, pupae or adults may undergo diapause (early stages) or hibernate (adults) during unfavourable periods. The pupal stage is the one which may remain dormant for longest - a desert moth pupa is known to have remained dormant for 16 years before producing a perfectly healthy adult! In univoltine species the adults are often on the wing for only a few weeks, generally either in spring or in autumn. Lay persons, and even biologists, often fail to understand the population dynamics of butterflies because they equate them with large mammals. A handful of rhinoceroses breeding remorselessly would reach about one hundred individuals after five years. The same handful of butterflies could reach 30 million within six months. The number of butterflies after five years would be simply astronomical! This has very important and obvious implications when considering the impact of butterfly collecting vis-a-vis conservation issues (see also “Predation and Parasitoids”, below). | ||||||
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5. VARIATION Like all biological entities butterflies are morphologically variable. This variation is of most interest in adult butterflies since we mainly make use of them in classification systems. Obviously there are differences between species (interspecific variation), although in some cases this may be very slight. Less obviously there is variation within each species (intraspecific variation), and in some cases this may be very marked. Intraspecific variation includes sexual, seasonal, geographical (subspecific), polymorphic, and individual variation. Sexual variation: In some species the sexes have almost identical wing markings but in others they are entirely different (sexual dimorphism). Seasonal variation: In a few butterfly species there are distinct wet season (summer) forms and dry season (winter) forms. Seasonal dimorphism, also known as seasonal polyphenism, is well illustrated by species belonging to the group of butterflies known as commodores (genus Precis). The gaudy commodore (Precis octavia) shows the most extreme seasonal dimorphism of any butterfly, the summer form being predominantly red and the winter form predominantly blue. For many years these seasonal forms were thought to represent two different species. Even when a summer and winter form were first found in copula this was interpreted as a hybrid mating! Today we know that by keeping the pupae at different temperatures we can breed out the two forms at will. Maintaining pupae at ‘boundary’ temperatures produces ‘mixed’ forms known as transitional forms (rarely transitional forms are also found in the field). Geographical variation: Small but consistent differences between geographically isolated populations of a particular species leads some taxonomists to classify them as subspecies. Given a sufficient period of time the differences between these subspecies become progressively more pronounced until the populations eventually become reproductively isolated (can no longer interbreed), when we have two distinct species. This phenomenon is known as allopatric speciation. Polymorphism refers to genetically determined colour forms, most often seen in females, within a species. This is best illustrated by the females of the mocker swallowtail (Papilio dardanus), a common butterfly that is widespread in the Afrotropical Region. There are dozens of named (and unnamed) female forms, all of which mimic distasteful or toxic butterflies. Polymorphism exists in many other species, but the reasons for this variation is usually unexplained. The last kind of infraspecific variation is individual variation. This is usually slight and does not interfere unduly with species identification. | ||||||
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6. COMMON AFROTROPICAL
SPECIES About 150 (4 %) of the more than 4000 Afrotropical butterfly species have what may be regarded as a ‘pan Afrotropical’ distribution. These pan Afrotropical species have been recorded from West Africa (Senegal/Guinea) to north-east Africa (Ethiopia) to southern Africa (South Africa). A number of these species are also found in Madagascar (49 species) and/or the southern Arabian Peninsula (66 species); these have been noted in parentheses.
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7. CLASSIFICATION Afrotropical butterflies (Superfamily Papilionoidea) are divided into five families but the Afrotropical skippers (Superfamily Hesperioidea) are restricted to a single family. These six families are: Papilionidae (swallowtails and swordtails), Pieridae (whites, yellows and sulphurs), Nymphalidae (brushfoots), Lycaenidae (blues, hairtails and coppers), Riodinidae (judys) and Hesperiidae (skippers). The number of species in each family in the Afrotropical Region is: 93 papilionids, 188 whites, 1 419 nymphalids, 1 700 lycaenids, and 515 hesperiids. Although there is fairly good, but not general, agreement about the correct designation of butterfly families, there is much controversy regarding the division of butterfly families into subfamilies. The validity of the tribal and subtribal taxon levels are also in a state of flux. Cladistic analyses, together with relatively new DNA techniques, will, hopefully, provide us with a more natural classification of taxa above generic level in the near future. Below is a classification of the families down to subtribal level (only taxa found in the Afrotropical Region are included).
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8. ADULT BEHAVIOURS Most species of butterfly obtain the nutrition they require for their activities in the form of nectar from flowers. This is particularly true of the papilionids, pierids and lycaenids. The males of many species, in all six families, are known to mud-puddle. This involves settling on muddy or damp sandy patches and the imbibition of large quantities of water. Every few minutes a drop of water is excreted. Thus muspuddling is not equivalent to drinking. It is known that the males extract salts from the water but what they require these salts for is not well understood. In some cases these accumulated salts appear to be passed to females at mating, so-called “nuptial gifts”. On hot sunny days very large numbers of males can be found mud puddling at a favoured ‘watering hole’. Females rarely mud puddle. Many nymphalid butterflies obtain all of their nutrients from fermenting fruit and so-called “sucking holes” in the boles and branches of trees. From these sources they obtain alcohol, which they use as an energy source. Sucking holes are usually engineered by beetles or other insects boring into the wood, resulting in the exudation of fermenting tree sap. The large and showy nymphalid genus known as charaxes (Charaxes spp.) are the best known alcohol-feeders among insects. There is often stiff competition among them at a particular “sucking tree” and they have evolved serrations on the leading edge of their front wings. The wings are used to batter each other and the peculiar sound can be heard from many metres away on a hot still day! Mammal dung, of carnivores, omnivores and herbivores, is also frequently visited. It is not unusual to find large numbers of butterflies imbibing moisture from piles of fresh elephant dung, especially where mud puddling is not an option. In tropical forests some species of skipper have been found feeding from bird droppings. The adults of some lycaenids (subfamilies Poritiinae and Miletinae) feed from the secretions (honeydew) of sap-sucking bugs known as hemipterans. A few groups of butterflies, such as the skollies (lycaenids of the genus Thestor), and many moths (e.g. emperor moths), do not feed as adults at all. Mating is a crucial function of the adult stage of butterflies and moths. Male butterflies use two main strategies to find mates – perching and patrolling. Perching behaviour involves the selection and defence of a defined territory, from a perch within the territory. These perches and territories are often on a geographical high point (often a hill top or ridge), but may be a forest or savanna tree, or a bush, or grass stem. Sometimes the perch is a stone or even a bare patch of ground. The particular perch that is selected depends very much on the particular species and terrain in which a population occurs. Species that select territories on high points are known as “hilltoppers” and the behaviour as “hill-topping”. Patrolling behaviour encompasses active coursing of males in search of females. Again this is species specific behaviour; patrolling species generally do not perch and vice versa. Some perching male skippers appear to use chemicals in their mate-location behaviours. Males of the ragged skipper (Caprona pillaana) have brush-like scales on their legs and extend these while perching. Males of Coeliades forestan possess a brush-like abdominal androconial organ with which they scent-mark leaves of bushes and trees in their territory. Even though these pheromones appear to be involved in mate-location much research needs to be done in order to fully elucidate the functions of these chemicals signals. Most moths locate mates by using volatile chemicals as homing signals. These chemicals, known as pheromones, are produced by a special gland at the tip of the abdomen of the female. Pheromones are relatively species specific and are able to attract males over a distance of several kilometres. The feathery antennae of many male moths are covered with chemical receptors that can detect the specific pheromone at concentrations measured in parts per billion. Recent research has indicated that some female moths produce electromagnetic waves that are picked up by the male antennae, similar to radar detection. Some moths are even capable of “jamming” the radar system that bats use to detect their prey! Because adult butterflies have the power of flight they are capable of both dispersal and migration. Dispersal is the active or passive emigration of individuals from the home range of a population in a random direction, whereas migration is mass movement of large numbers of individuals in a specific direction. Migration is a complex biological phenomenon that is incompletely understood. The huge migrations of white butterflies (mainly the brown-veined white, Belenois aurota, and the African migrant, Catopsilia florella), in a north-easterly direction, in southern Africa is probably caused by over-population in populations originating from the Karoo and Kalahari regions. Here numbers of larvae reach such densities that larval food plants are completely denuded of foliage, causing the stressed adults to ‘trek’ in search of ‘better pastures’. Migration ‘hormones’ probably induce the behaviour and magnetite biological compasses in the head of the butterfly, possibly provide the means for navigation. However, the direction of flight that is invariably chosen is apparently a complete mystery. | ||||||
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9. PREDATION AND
PARASITOIDS Female butterflies, depending on species, are capable of laying from 50 to about 500 eggs. For a population to remain numerically stable a particular female must provide two adults to replace herself and her mate. This implies that there is a mortality rate of 96% or greater. This staggering carnage occurs mainly in the early stages. In one population of butterflies that I studied more than 90% of the eggs that were laid were parasitized by minute wasps with a wingspan of less than a tenth of a millmetre (they looked like tiny specks of dust with the naked eye). Larvae and pupae are decimated by diseases caused by viruses, bacteria and fungi, hordes of parasitic wasps and flies, and carnivorous insects and vertebrates. Vertebrate predators include frogs, reptiles, birds and even mammals. In respect of the latter one only has to think of the fondness that some African tribes have for mopani moth caterpillars. Most adult butterflies and moths also provide tasty morsels for an army of hungry invertebrates and vertebrates. The often virulent attacks that butterfly and moth collectors must endure from ignorant, albeit often well-meaning, lay persons and the conservation fraternity would be laughable if it was not so counter productive (see also “Conservation”, below). |
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10. DEFENCE STRATEGIES From what has been said in the section above one would think that butterflies are powerless to defend themselves. This, of course, is not so and they have developed many fascinating survival strategies. Eggs are often deposited in concealed places or may be covered by sticky substances that may trap the wings of would-be parasitic wasps. The sheer numbers of eggs may saturate the predators ability to use them. Larvae and pupae are often superbly camouflaged. Some larvae closely resemble lichen and moss encrusted twigs, others resemble shoots and leaves; some even closely resemble fruits, so escaping detection by the beady eyes of lizards and birds. Adult butterflies may be shaped and coloured like dead leaves, and when settled among dead leaves on the forest floor may be virtually invisible. Adult butterflies often have tails projecting from their hind wings – presumably these act as ‘false antennae’, directing an attack away from the vulnerable head end. Some lycaenid butterflies have elaborate false heads and antennae, complete with false eyes, on the ends of their hind wings. In order to enhance the effect of the false head they often settle head down and rub the closed hind wings together, almost inviting a potential predator to attack the ‘wrong end’. If deception and other passive strategies do not work then one can always resort to aggressive strategies, based on the maxim that the best method of defence is attack. For butterflies attack takes the form of poisoning the predator. The classical example is the nymphalid subfamily Danainae (monarchs). Monach caterpillars feed on milkweeds (Aclepiadaceae) which contain heart poisons known as cardiac glycosides, toxic to vertebrate predators, such as birds. In addition adult monarch butterflies ingest pyrollizidine alkaloids from damaged plants that contain them. These are liver toxins. Both the early stages and adults are brightly coloured, displaying so-called “warning colouration”. Combinations of black, white, yellow and red are usual. Darwinian selective pressures over millions of years have resulted in a number of unrelated palatable species coming to resemble their toxic models. Groups of similar models and mimics are known as mimicry rings. One of the most extraordinary mimicry rings involves the African monarch, common diadem, mocker swallowtail, common mimic acraea, boisduvals false acraea, and others. | ||||||
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11. AS RESEARCH TOOLS Butterflies and moths, because they are easy to work with, are the subject of numerous studies dealing with basic biological processes. Recently they have become an important tool in biodiversity and environmental impact studies. This is because they are taxonomically diverse, and are the best known insect group, thanks largely to the efforts of amateur butterfly collectors. Because they are highly visible and relatively abundant, data is easily collected and compared with existing data sets. | ||||||
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12. PESTS There are no major butterfly pests, but there are a number of very serious moth pests. In Africa the most important butterfly pests are the African clouded yellow (on lucerne), citrus swallowtail (on citrus), the long-tailed pea blue (on the seeds of pulses) and the coffee playboy (on coffee beans). |
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13. CONSERVATION As is the case with most living species the impact of man is taking an ever increasing toll on butterflies and moths. Habitat modification and destruction due to human activities, including the introduction of alien invasives, is the major threat. It is particularly important to those species which have small, local populations because they require very specific habitats. Even minor modifications of these habitats might result in the extinction of that species. Knowledge about which species are under threat, what the threats are, biological and taxonomic data, and conservation needs is provided by amateur collectors. Their advice is crucial for the conservation authorities who are legally charged for the implementation of appropriate measures. As I have emphasized throughout these notes it is important to educate the public on this issue. Far from denigrating and even criminalizing butterfly and moth collecting children, especially, should be encouraged to collect and study these beautiful creatures. The bottom line is that butterflies and moths do not have a future if collectors do not. | ||||||
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14. MYRMECOPHILY The life cycles of many lycaenid butterflies are bound up with ants. This is known as myrmecophily (myrmos = ant; philos = to love). The association between lycaenid caterpillars and ants, if it occurs, may be casual and non-essential (facultative myrmecophily) or it may be essential for the completion of the life cycle (obligate myrmecophily). In some cases the larvae are entirely phytophagous, in others they are partially phytophagous, and in still others they are entirely carnivorous (parasitic on ant brood). A few lycaenid caterpillars are fed directly by the worker ants, a process known as trophyllaxis. In a few groups of lycaenids the larvae are associated with hemipterans such as scale insects and membracids. Hemipterans, in turn, are frequently closely associated with ants, the latter tending them and ‘milking’ them for their sweet honeydew. This close association between lycaenid larvae, ants and hemiptera has probably evolved because both lycaenid larvae and hemiptera utilize the soft, nutritious growing shoots of plants. Virtually all lycaenid species whose larvae use this microhabitat have anatomical specializations that allow them to survive possible aggression by hemipteran-tending ants (for the ants the hemipterans are ‘sacred cows’). Scattered microscopic glands in the larval cuticle, known as perforated cupola organs (PCO’s), are capable of producing ‘ant appeasing secretions’. Other lycaenids have a honeydew-producing gland (dorsal nectar organ) which is ‘milked’ by ants. All lycaenid caterpillars appear to have a cuticle which is up to 10 times thicker than that of caterpillars not associated with ants. Further specializations in some groups include eversible tentacle organs (TO’s) and even vibratory papillae. Lycaenid larvae are thus able to communicate with their associated ants by chemical as well as auditory systems. Larvae of the lycaenid genus Lepidochrysops feed on the developing seeds of flowering shrubs for the first two larval instars. After this they induce a specific species of ant to pick them up by emitting a chemical analogue of the ant’s brood. The ant carries the larva into its nest and drops it with the brood. The lycaenid larva then becomes carnivorous on the ant brood. This is just one example of the suite of possible ant-lycaenid interactions that are known to occur. A few lycaenid groups have become hemipterophagous. In southern Africa this is known to occur in Basutu skolly (Thestor basuta), the purples (Aslauga spp.), the woolly legs’ (Lachnocnema spp.) and the lemolea harvester (Spalgis lemolea). | ||||||
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15. ORGANIZATIONS AND
LITERATURE The Lepidopterists’ Society of Africa has a virtual home of lepidopterists interested in the Afrotropical fauna at www.lepsoc.org.za. Amongst various activities of the society is the publication of its quarterly journal Metamorphosis, containing a blend of both scientific and popular articles. The bibliographies in the main body of the encyclopaedia contains nearly six thousand literature references, including all the books that have been published on Afrotropical butterflies. |
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