|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”.
There is actually no real distinction between butterflies and moths but, generally, butterflies fly during the day (are diurnal), are brightly coloured, have a club at the end of the feelers (= antennae), and have naked pupae (moth pupae are often cocooned). Skippers are, in some respects, in between moths and butterflies because they often fly at dawn or dusk (are crepuscular), have drab colours, the ends of the antennae have a club often followed by a hook, and pupation occurs in a rudimentary cocoon between folded leaves. A few moths, particularly in the families Arctiidae and Sessidae, are diurnal, brightly coloured, and have clubbed antennae.
|2. DIVERSITY AND SPECIATION
There are more than 18 000 described species of butterflies and skippers in the world, and new ones are still being discovered. There are probably at least ten times as many “moth” species, many of which must still be discovered and described. A rough estimate would be at least a quarter of a million species of Lepidoptera. Many of these will become extinct even before they have been discovered, largely because of the impact of habitat modification and degradation by expanding human populations and activities.
The Afrotropical zoogeographical region (Africa south of the Sahara, the southern Arabian Peninsula, and the off-shore islands, including Madagascar) boasts just over 4 000 described species of butterfly and skipper (about one fifth of the world total).
Species diversity of butterflies in any particular geographical region is related mainly to vegetational diversity. This, in turn, is dependant mostly on climatic and geomorphological factors. Plant diversity is generally highest in areas of high rainfall, high temperatures (low altitudes and latitudes), and variable landscapes. Butterfly diversity (and abundance) is therefore highest in wet, tropical, lowland forest and lowest in dry, cold, polar deserts. On one forested mountain, a few hectares in extent, in Cameroun, more than 1 000 species of butterfly have been recorded, while not a single species is found on the continent of Antarctica. In South Africa the Golden Gate Highland National Park and Blyde River Canyon Nature Reserve are of similar size. The floristically less diverse Golden Gate has fewer than 100 species whereas the floristically rich Blyde Canyon has about 300. Butterfly diversity thus generally mirrors overall biological diversity for any particular region, one of the reasons why they are a popular model for various branches of scientific inquiry. A striking exception to this rule is the Cape Floral Region, which has nearly 9 000 plant species but a relatively depauperate butterfly fauna. The reason for this is that butterfly larvae mainly utilize the meagre sub-tropical elements of this flora, indicating that the butterflies and the fynbos plants evolved separately.
|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.
|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).
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.
|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.