To migrate or not to migrate?
Text Steve Woodhall Photographs Steve Woodhall and others
First define ‘migrate’
We are all familiar with fish, mammal, and bird migrations. The ‘Sardine Run’ off KZN. Wildebeest on the plains of East Africa. The far-travelling Arctic Tern or Amur Falcon. Even tiny birds migrate – as witness the Lesser Whitethroat that took a wrong turn and ended up in South Africa instead of England! Those birds overwinter in the Sahel and other warm dry regions and move back to the cooler climes of northern Europe during their summer. Birds ringed in the southern hemisphere are often recovered in the northern hemisphere, and vice versa.
Mammals and birds go ‘there and back again’, like Bilbo Baggins the Hobbit. Like him they live for more than one year (but not usually as long). Unlike him they do it every year. Insects, on the other hand, very rarely live for more than one year, or even one season. But we often see them travelling in one direction, sometimes in their millions. We refer to these as ‘migrations’, but is that in the same sense that mammals, birds, and fish migrate?
To ‘migrate’ simply means ‘to move from one part of something to another’. In the sense of animals, there is an added meaning – they evolved to do this to benefit from temporary peaks in food abundance created by transient seasonal changes in habitats. Such behaviour has evolved in a wide range of disparate species; not only birds, mammals, and fish, but also reptiles and many types of arthropods – including insects.
All this migratory activity is happening today – so it’s a mere skin on the surface of what’s happened in the past. Insects have been around for far longer than reptiles, birds, or mammals; they were the first animals to fly. The ancestors of today’s butterflies and moths probably appeared at the same time as flowering plants – the late Jurassic and early Cretaceous period, around 150 million years ago. Dragonflies have been around for even longer. Interestingly, birds arrived around the same time as Lepidoptera. But planet earth has had seasons since she formed, and the movement of landmasses caused by tectonic plates has been going on all this time. There’s plenty of time for migratory habits to have evolved and changed.
Even in the relatively recent past – about 10 million years ago – the biodiversity of earth would have looked very different to what it does today. Africa’s vegetation was changing from almost total forest to the mosaic of savanna and forest we have today. The southern tip of the continent was cooling due to the icing over of Antarctica and the circulation of cold polar air. What effect this had on migratory behaviour of animals is known – mass movements of grazers. We also know that a subgroup of the great Apes moved from arboreal to terrestrial behaviour – eventually becoming us!
There may well have been butterflies in the past that were as widespread as the Painted Lady is today, but whose preferred (and widespread) habitats became fragmented. This could have caused them to become more sedentary as hostplant opportunities became harder to find. Uplift of mountain ranges causes stratification of habitats, with butterflies and moths becoming ‘trapped’ in isolated patches of suitable vegetation surrounded by inhospitable barriers. This can cause them to lose their migratory behaviour and eventually evolve into new species via genetic drift.
As Africa aridified, savanna occupied a greater area with the expansion of the ‘miombo’-type woodlands currently typical of Zambia and Zimbabwe. The process wasn’t smooth and consistent; there was a lot of seasonal variability, increasing as aridification increased from the late Miocene. Grasses became more widespread, leading to increases in grazing herbivores, and more frequent fires. The modern savanna and grassland biomes became established between 8 and 3 million years ago, and fynbos and karoo over a similar timeline.
All these changes created ecological niches as well as dispersal pathways, and butterflies and moths adapted to take advantage. One of these was the evolution of ant association, which has evolved many times in the Lycaenidae (blues, coppers etc) – to survive lengthy dry seasons by sheltering inside ants’ nests and preying on their young. Recent studies have suggested that this process took place over the past 5-20 million years, with successive dispersal, speciation, and extinction events. These extreme niche specialists are the opposite of the wide distributions of typical migratory species. Typically, they are small, weak-flying butterflies with specialised, narrow ecological needs. Ant association is not the only type of specialisation seen. These lifestyles are known as stenoecious, because they occupy narrow ecological niches, as opposed to the euryecious species that can tolerate a wide range of habitats.
Locust swarms are perhaps the best-known African insect migrations, but many familiar dragonflies are also migratory.
The Wandering Glider, Pantala flavescens, has an annual multigenerational migration between Africa and Asia, of about 18000km, with individuals travelling up to 6000km, and as high as 6000m.
The also-migratory Amur Falcon Falco amurensis, photo courtesy of Trevor Hardaker, probably relies on Pantala flavescens for food when crossing the Arabian Sea.
Dispersal versus migration? Not all who wander are lost.
Lepidoptera can fly, and therefore can move around at will. So why do some species seem to wander aimlessly from flower to flower, and others show strong migratory behaviour? And why do some others hang around close to where they were laid as eggs, and seldom move far away?
‘True’ migrants, whose north-south patterns resemble those of birds.
The well-known Painted Lady, Vanessa cardui, is a strongly migratory butterfly that tends to move in a particular direction in specific seasons and is one of the few known to make a large migratory ‘leap’. They are robust, fast-flying insects that can travel for long distances.
The American Monarch, Danaus plexippus, is famous for its multigenerational round trip between Canada and Mexico. It flies northwards in spring and summer, and southwards in autumn. These are large enough to be marked using wing stickers, rather as birds are ringed – making it easier to track their movements. Studies have shown that they do this over up to five generations, one of which overwinters in diapause in northern Mexican forests in the huge numbers that have become a tourist attraction. This butterfly is now dispersing westwards across the Pacific and Indian Oceans and is now resident in New Zealand and Mauritius – but that’s another story.
Painted Ladies have a much wider range than the American Monarch; they are the world’s most widespread butterfly. They are found all over Africa, Europe, and Asia, as well as North America. That population behaves similarly to the Monarch, with one important difference; there is no winter diapause, simply a succession of year-round generations, usually six per round trip. Painted Ladies have a wider ‘hostplant spectrum’ than Monarchs. Their larvae are known to use many of the widespread Asteraceae (Daisy family) as well as many of the Malvaceae. They have been recorded from as far north as Svalbard near the Arctic Circle, and Marion Island, close to the Antarctic.
The migratory patterns of the African/European Painted Lady populations are now known to be somewhat more complex than those of the American Monarch. These patterns change in response to wide-scale rainfall fluctuations such as El Niňo. Recent research (observational and stable isotope analysis) has shown that in Europe as in Africa, they follow the rainfall patterns that result in a ‘movable feast’ of large amounts of available larval food. High rainfall in savanna areas like the Sahel cause a peak in host plant availability that leads to mass emergences of millions of individuals, which in the northern hemisphere spring, March to May, migrate north. Their larvae are one probable reason why the Sahel is so popular with overwintering birds. One theory goes that such migrations are a major factor in dispersal of biomass around the globe.
Retrograde migrations of Painted Ladies from Europe to tropical Africa, once thought unlikely, are now known to occur regularly. Individuals are thought to be capable of flying from Iceland to the Sahel, and British Painted Ladies have been detected flying south at extremely high altitude – over 6000m. It is possible for an adult Painted Lady to travel for over 4000km! They even migrate at night as do moths.
In South Africa they often emerge in May to July and in cooler areas may be the only butterfly on the wing. Our southern population also migrates northwards, ‘following the rains’, to the tropics where they may mingle with individuals from elsewhere in Africa, and Europe. However, their migratory behaviour is not as well-studied as the northern hemisphere population. In the tropics, the generational length (because of high rainfall and warm conditions) is much shorter than in higher latitudes. And as the high rainfall intertropical convergence zone moves back and forth across the tropics, opportunities for mating between specimens of northern and southern origins probably exist, because these butterflies constantly mate (often with more than one partner) and lay many eggs over a long period of time.
To explain fully all the details of Painted Lady migratory behaviour would take a book! For those who are interested, here are some useful websites:
http://www.butterflymigration.org/research.html
https://academic.oup.com/biolinnean/article/120/2/274/2954916
https://royalsocietypublishing.org/doi/10.1098/rsbl.2016.0561
It’s very heartening to see the role that Citizen Scientists are playing in some of these projects.
Convolvulus Hawkmoth, Agrius convolvuli, is another strong migrant.
The fast-flying Silver-striped Hawkmoth, Hippotion celerio
The rare and spectacular Oleander Hawkmoth, Daphnis nerii
Moths also migrate, but they don’t really have a reputation as such. Because they are largely nocturnal people don’t notice them when they fly in numbers. Large swarms do, however, often fly at night. Bright lights attract them, and sometimes thousands are attracted to these at petrol stations or isolated bush lodges and farmhouses. The photo was taken when a large swarm of Convolvulus Hawkmoths arrived at a makeshift light trap set up on the Wakefield Nature Reserve near Nottingham Road in the KZN Midlands. They accounted for perhaps 99% of the numbers; the smaller but also strong-flying Silver-striped Hawkmoth Hippotion celerio accompanying them. Such multi-species swarms have been witnessed elsewhere – with the occasional Oleander Hawkmoth Daphnis nerii or Death’s-Head Hawkmoth Acherontia atropos included.
Little is known about Hawkmoth (Sphingidae) migratory behaviour, but many are noted migrants. These species are native to Africa and parts of Asia. They are powerful, rapid fliers – closer to small birds in their power to weight ratio than most butterflies. If birds as small as the Lesser Whitethroat can fly a third of the way around the globe in less than a year, it’s probably reasonable to assume that Hawkmoths can do this too. Apart from the Death’s-head, all feed on nectar during flight, from flowers with long tubular corollae. Certainly, migrations of all four species regularly reach Europe. They are all rare in the British Isles, but when I was a boy growing up there, we sometimes saw Convolvulus and Silver-striped Hawkmoths. Oleanders and Death’s-Heads were known to occur there but remained a schoolboy dream until I moved to South Africa! All four species have several broods and are known to be able to overwinter as pupae in Europe, albeit to a variable degree. They are more difficult to study than Painted Ladies, but the chances are that their migratory behaviour is just as complex.
Dispersal versus migration? Multi-year dispersal.
Euryphura achlys, which is known by more than one common name but for now let’s use ‘Mottled Green Nymph’. It’s a very rare butterfly in South Africa – is it a migrant?
Mottled Green Nymphs are common in warmer areas of Africa, especially in the tropics. South Africa is on the extreme southern edge of their range. Local numbers appear to fluctuate with the intensity of the rains. In drought years they are almost never seen, but after good rains they regularly turn up in northern areas like Manguzi Forest and Tembe Elephant Park. Occasionally one is found as far south as oNgoye, and recently one was photographed in Lekgalameetse Nature Reserve, many kilometres west from the coastal hinterland where they are usually seen.
So, what is going on here? The host plant, African Coca-tree, Erythroxylum emarginatum, is found almost as far south as East London. It is known to grow along river courses and the butterfly is usually found in such habitat in eastern Zimbabwe. Is there a background population in northeast South Africa that is very scarce in dry periods, but still present if never seen because no-one is looking? Or does the butterfly disperse southwards and westwards in wetter spells, only to die out in droughts? Technically, this southwards movement is a migration, but it occurs gradually over several years and the numbers are too small to be obvious to casual observers.
Charaxes (was Euxanthe) wakefieldi, the Forest Queen, male photographed at Umdoni Park, near Pennington.
Forest Queen is another tropical butterfly that is appears to be non-migratory but is steadily dispersing southwards as the climate warms and suitable conditions are found further south. In the past this was a Zululand specialist with a few populations in coastal bush north of Durban. Nowadays it is commonly found on the Bluff, has been seen in the Upper Highway area and has reached as far south as Port Edward. Its local host plant is Dune Soapberry, Deinbollia oblongifolia, which occurs in coastal thickets and forests down into the southern parts of the Eastern Cape. The butterfly clearly still has scope for further southern dispersal.
‘Burst’ dispersals.
Perhaps South Africa’s best-known migratory butterfly is the Pioneer Caper White, Belenois aurota.
Rather than moving in a particular compass direction, some butterflies appear to ‘burst’ in all directions from a certain starting point. The Pioneer Caper white appears to do this, because in Durban they are seen flying from west to east, in Johannesburg towards the north-east, and in the southern Cape, due south.
There is surprisingly little known about this species’ habits, other than that it is regularly seem moving across country in a particular direction, in swarms sometimes numbering in millions. What we do know is:
- South Africa isn’t the only area where they are found. They occur all over Africa and Asia as far as the Himalayas. In southern Africa the main centre of population origin seems to be the Kalahari.
- There are areas where they seem to be sedentary rather than migratory. In such areas their host plants, members of the Caper family, are prevalent. Females lay large batches of eggs; multiple generations can build up in a few months to huge numbers, overwhelming their natural predators.
- The numbers often build to the point that the host plants are defoliated.
- A proportion of adults appear to anticipate when the next generation will run out of food. Instead of staying close to the host plants, they disperse in all directions from the point of overpopulation. What triggers this is currently unknown, but it is the subject of some in-depth research.
- They appear to fly in a more-or-less straight line from their point of origin.
The question is – are these butterflies truly migrating, or simply dispersing until they find new suitable habitat? They don’t seem to follow a clear, parallel migratory path, it’s more of a ‘sunburst’ pattern. Do they mingle with East African, Arabian, or Asian relatives? We don’t know, but looking at the Painted Lady, anything is possible…
Catopsilia florella, African Migrant
No discussion of migratory African butterflies would be complete without the ‘African Migrant’! This is another species that uses a widespread genus of host plants – Senna. In fact, its use of the intra-African invader species Senna didymobotryia Peanut-butter Cassia has helped it expand its range greatly. Like other migrants it appears to follow bursts of greenery that follow seasonal rains.
There are lots of butterfly species that don’t paint the country white with their numbers. In fact, most species are probably migratory to some extent. The conditions that lead to sudden bursts of butterfly numbers can be more complex than rainfall patterns or changes in the prevailing winds. As I mentioned in a previous article, predator activity and rainfall changes affect, probably, all insect species. That article mentioned the next butterfly.
Sevenia boisduvali, Boisduval’s Tree Nymph, is a butterfly that can have a population explosion in one’s own garden!
These are just a few of the thousands of individuals that can emanate from just one small (4m high) defoliated Duiker-Berry tree Sclerocroton integerrimus. One sometimes sees huge concentrations of these in the bush, to the extent that the tree looks like it has brown leaves… and then they just disperse…
Coeliades libeon, Spotless Policeman, is one of those strange butterflies that are normally incredibly rare, then suddenly turn up in massive numbers, seemingly out of nowhere…
This photograph was taken some years ago in Port St. Johns. Spotless Policemen were everywhere… countless millions of them. Every flowering bush was covered with them and a short drive to Ntafufu up the road led to a clogged radiator and a risk of an overheating engine. Yet the putative local host plant, Drypetes gerrardii, Forest Ironplum, was untouched with no sign of eggs or pupae. I heard later that they hung around for another few weeks then disappeared as suddenly as they appeared. A few larvae turned up on Drypetes gerrardii much later.
Other Coeliades occasionally do this. Many years ago, Coeliades anchises, the One-pip Policeman, was reported from the Mkuze River in such numbers. Living in Johannesburg at the time, I could only get there a week later… and there wasn’t a single one to be seen.
Butterflies that DON’T migrate… at least not so you’d notice.
Aloeides penningtoni, the Natal Russet, is an example of a widespread stenoecious butterfly.
Natal Russet occupies small niches and like all its genus (and many butterflies in the same family, Lycaenidae) is ant associated but with plant eating larvae. They probably feed on legumes such as Lotononis sp, because the adults are always found near clumps of this. It lives in metapopulations – groups of small colonies in suitable niches situated close to one another, with some localised dispersal of specimens from colony to colony. There are several populations in the Upper Highway area, and it is found widely in mid-altitude grasslands along the lower KZN escarpment. There is probably some short-range migration from niche to niche as localised extinctions occur, caused by drought or heavy grazing. Because the larvae live underground in ants’ nests, they can survive veld fires.
Lepidochrysops pephredo, Estcourt Giant Cupid, a rare lycaenid. This male is perching territorially on a dry grass stem at Spitskop near Estcourt.
Lepidochrysops variabilis, Variable Giant Cupid, photographed close to one of the few colonies of Lepidochrysops pephredo.
Lepidochrysops variabilis, Variable Giant Cupid, photographed hundreds of kilometres away in the Little Karoo at Lootsberg Pass between Middelburg and Graaff-Reinet.
These two species of Giant Cupid appear superficially similar, but there are important differences. Estcourt Giant Cupid has a more vivid white band across the hindwing underside, but it has a similar grey-brown upper side. It is only found in a very small range in the KZN Midlands; around Estcourt, Mooi River (where it is now seldom seen) and a remote colony in the Royal Natal National Park. Conservationists have been very worried about this butterfly because it had vanished from several of its haunts.
Variable Giant Cupid, on the other hand, is found across a vast range of montane habitats from the Western Cape, across the Eastern Cape to KZN, Gauteng and Mpumalanga. As its name suggests, its appearance is variable – mainly in the appearance of spots on the forewing underside.
Both species have phytopredacious larvae – that is, the eggs are laid on flowers of the host plant, and the larvae feed on the ovaries and developing seeds until the third instar. At this stage, the larva is carried into an underground nest of the Hairy Sugar Ant, Camponotus niveosetosus. Whilst in the nest they feed on the ant brood, until they reach the fourth (final) instar. At that stage they enter diapause until pupation, upon which the cycle begins again. The butterflies are usually univoltine (single brooded); they only appear on the wing once a year, usually in spring. This kind of behaviour has only evolved twice in the Lycaenidae. Once in the Africa-centred genus Lepidochrysops, once in the Eurasian genus Phengaris. Both have a tendency to live in small colonies that form part of larger metapopulations. There are 137 Lepidochrysops species in Africa, 49 of which are found in South Africa.
Variable Giant Cupid is a stronger flier which frequents the summits of hills and mountains whereas Estcourt Giant Cupid is a relatively weak flier found on the lower slopes. Even where they fly together, the Estcourt Giant Cupids are found on the hillsides, not the absolute peaks.
Estcourt Giant Cupid only has one hostplant, Cat’s Whiskers, Ocimum obovatum, whereas Variable Giant Cupid larvae can use several plants – Selago corymbosa, several Ocimum and Salvia species.
Ant association and other specialised life histories have been described as ‘evolutionary dead ends’. As the colonies become more separated and isolated, extinction caused by single catastrophic events becomes more likely. From these two species, Variable Giant Cupid appears to have the advantages of being able to disperse and use a wider range of host plants. Its IUCN Red Listing is LC (Least Concern). Estcourt Giant Cupid, on the other hand, is officially a threatened species – its Red Listing is VU B1ab(ii,iii,iv,v)+2ab(ii,iii,iv,v). Its habitats are under threat from overgrazing by cattle (which destroys the host plants). The increasing fragmentation of the metapopulation into widely scattered areas surrounded by habitat made inhospitable by human activities reduces the gene flow essential to its survival. Members of the Lepidopterists’ Society of Africa have embarked on an awareness program amongst farmers in its last stronghold around Lowlands. Several hitherto unknown colonies have been recently discovered, and the landowners advised on how to manage them to the butterfly’s advantage. This should help arrest or even reverse its decline.
Capys penningtoni, iNkomasi Protea, is one example of a species approaching a dead end. It is extremely rare and getting rarer. Its Red List status is Critically Endangered – CR C2a(i).
iNkomasi Protea is another specialised lycaenid, whose larvae use the immature seeds of Common Sugarbush Protea caffra caffra or Dwarf Grassland Sugarbush P. simplex. Females lay their eggs on the flower buds and the larvae burrow in and eat the seeds in the ovary. Protea Butterflies are widespread across Africa, 18 species in all, found wherever Protea plants grow – even as far away as Nigeria. We have 3 of those species in South Africa – the other two are found over most of the country.
Bulwer Mountain, or Amahaqwa, is one of the last places one can hope to see iNkomasi Protea, males hilltopping on the main or subsidiary summits. Fire-damaged specimens of its host plant can be seen growing in the grassland between the rocks.
Such Protea savanna is under threat from alien plants such as American Bramble and bracken, which intensify fires in the vicinity of the trees and damage to a greater degree than normal grass fires.
iNkomasi Protea is only found in suitable Protea savanna in an arc of mountains between 1000m and 2100m in the catchment area of the iNkomasi River in the Drakensberg. As well as the threats to its host plant, the invasive Harlequin Ladybird is common in its habitat; they are often seen on the flower buds, and they are known to use lepidopteran eggs as food. Although there is no direct evidence as such, it is likely that the more intense fires, and the predation by the ladybird, are having a synergistic effect in harming the butterfly population.
It resembles the smaller, more brightly coloured, more widespread Russet Protea, Capys disjunctus disjunctus, which uses more than six species of Protea including the ones that Capys penningtoni uses. Colonies may be found in the northern Drakensberg in similar habitat. This may be another example of a speciation event driven by a population of a widespread species becoming ‘trapped’ in an area where gene flow between pockets of a metapopulation has been prevented by lack of suitable habitat outside its home range.
Dingane’s Widow Dingana dingana male upper and underside
Lycaenidae is not the only butterfly family to have extremely range limited, threatened species. Several of the subfamily Satyrinae (Browns, Ringlets, Widows etc) in the Nymphalidae fall under this category. Widows are a case in point. They are confined to South Africa. Dingane’s Widow was until recently thought to be a single species with a range of subspecies scattered across the eastern escarpment grasslands. Now it is known to be a complex of seven species that stretches from the KZN Midlands (where Dingana dingana is found) up to the Wolkberg and west to the Waterberg. They share a love for the nectar of Asclepias adscendens (Pompom Cartwheels) as shown by the underside photo. All have grass-feeding larvae and microclimate appears to be what limits the dispersal of these butterflies. Dingane’s Widow is not the rarest (that’s the Stoffberg Widow, Dingana fraterna) but lepidopterists had become very worried about it, because its range was shrinking. Fortunately, its range is roughly the same as that of Estcourt Blue, and has a similar Red List status: EN B1ab(i,ii,iii,iv,v)+2ab(i,ii,iii,iv,v). In several of the newly discovered spots they fly together.
Widows prefer steep rocky slopes with grass growing between the boulders where it is protected from herbivores. The adults only fly during the cool hours of the morning, so global warming is a threat to them. Their larvae are known to take almost a year to grow to full size (the butterflies are univoltine) and they shelter by burrowing into the base of grass clumps and pupating there. Nonetheless, overgrazing by cattle and goats, wildfires, and invasion by volunteer pine trees (or deliberate afforestation) are risks. Fortunately, Dingane’s Widow is covered by the same farmer awareness campaign that benefits the Estcourt Blue.
We could not have an article like this without mentioning one Upper Highway lycaenid special!
This male Yellowish Amakosa Rocksitter, Durbania amakosa flavida, is another example of a butterfly genus confined to South Africa, but in this case, there are two quite well-defined species, one of which is split into seven subspecies. Yellowish Amakosa Rocksitter is one of these, and it’s confined to two main population centres in eastern KZN, with a Red Listing of EN C2a(i) – endangered. One population is found around oNgoye and Nkandla Forests in Zululand, and the other around Durban. This population (most likely a fragmented metapopulation) is under threat from human activities such as building and infrastructure development, and it appears to be diminishing in numbers. Fortunately, two new colonies have recently been discovered by Mark Liptrot, an energetic member of Kloof Conservancy and the Lepidopterists’ Society. The photographed specimen is from the Monteseel colony, which is under threat from a residential development. Subspecies of Durbania amakosa are found from the Eastern Cape (Makhanda) to Mpumalanga (Mariepskop) below the eastern escarpment from the mountains to the sea, where suitable habitat (moist montane grassland with exposed lichen-covered sandstone rocks) exists. (Note: recently the oNgoye and Nkandla populations were determined to be the much commoner Natal Amakosa Rocksitter, Durbania amakosa natalensis.)
There are 13 recognised species/subspecies of Rocksitter in our country. All have similar life histories that set them apart from other lycaenids, including most of the subfamily Poritiinae. The adults cannot feed, lacking functional mouthparts, and they have very weak flight, seldom wandering far from their home rocks. The females lay eggs on the rocks amongst the larval food, which is rock lichen. Lichens are comprised of a fungus living in symbiosis with algae and/or cyanobacteria, and the appearance and chemical composition appears to be stable for a given combination. We know that the larvae digest the algal (or cyanobacterial) components. The nutritional value is low, and the larvae take a year to develop to the pupal stage, which is quite short before the adults emerge.
Although there are other Poritiinae related to the Durbania, like Alaena, which are widespread in Africa and will also feed on rock lichens, it’s uncertain what has driven the South African populations to disperse so widely, then adapt to their current appearance (which is very different to Alaena) and begin to speciate. Their undersides are exquisitely camouflaged against their home rocks, even to the orange (presumably toxic) cyanobacterial patches that appear to indicate where one can expect to find them. The butterflies are distasteful, exuding a bitter-smelling oil when molested, which possibly comes from the larval food. Poritiinae are found commonly across the Afrotropical forests and into Asia, and they often feed on cyanobacteria. I have a theory that in the distant past, a population of proto-Rocksitters dispersed into what is now South Africa and became ‘trapped’ in a nutrient-poor rocky, sandstone habitat, before dispersing when suitable habitat became more widespread during a cold, wet climatic period. When the climate warmed and the suitable habitat became fragmented, the populations split into smaller colonies and genetic drift led to speciation. The situation is probably similar with the Dingana Widows, whose distribution is similar. It’s difficult to imagine any gene flow occurring nowadays over their rather large range. How many extinction and dispersal events have happened over the past 5-8 million years is a matter for the new breed of DNA scientists…
Finally, we come to a butterfly that appears to have become specialised out of existence. The genus Orachrysops (Cupids) is sister to the Lepidochrysops (Giant Cupids) and is mainly native to the moist eastern grasslands of South Africa. The larvae are all legume feeders; they are associated with Camponotus ants and appear to have evolved to feed off the nutritious bacterial nodules found on their host plants’ roots. KZN has several of these butterflies, notably the Karkloof Cupid Orachrysops ariadne, which is under threat of extinction due to habitat fragmentation and overgrazing. Two species adapted to areas in moist coastal fynbos, and one of them appears to have been driven into a corner from which it could not escape.
Male Brenton Blue (now Brenton Cupid) underside. Live upperside photos are extremely rare because the males seemed never to bask in the sun, wings-open.
Female Brenton Cupid upperside. The females’ upper wing markings are much duller in colour than the males’, being mostly brown. They were happy to pose wings-open.
The Brenton Blue Nature Reserve was one of the first dedicated Butterfly Reserves in Africa. It is quite small – 1.6 hectares – and very carefully managed to protect the butterfly and its habitat.
Unfortunately for Orachrysops niobe, it was always very rare; Roland Trimen discovered it when visiting Knysna in 1858, but it was not seen again until Dr Jonathan Ball rediscovered it at the nearby Nature’s Valley resort in 1977. Housing pressure led to its disappearance there in the late 1980s. Dr Ball sighted one at the last locality, at Brenton-on-Sea, which was confirmed in 1991 by Ernest Pringle. Even then, it was under threat from development and there was a tremendous fight to save it from the bulldozers. To learn more, visit http://www.brentonbluetrust.co.za.
Its ecology was very complex with several factors essential to the butterfly’s survival. One was the host plant, Indigofera erecta, on whose young shoots and buds the female laid eggs, from which larvae emerged to feed on the shoots and flowers before moving underground to feed on root nodules created by nitrogen-fixing bacteria.
Another was the host ant, Bayne’s Sugar Ant Camponotus baynei, which milked aphids living on the roots of the host plants, in temporary nests with the butterfly larvae.
Also of vital importance were Candlewood thickets, Pterocelastrus tricuspidatus, in which the ants had their permanent nests. These had to be kept under control to prevent them shading out the vital Indigofera plants.
Plans existed to extend the Reserve to 15 hectares, but they came to nothing in July 2017 when the disastrous Knysna wildfire destroyed all the Candlewoods as well as the Indigofera. There were clearly some pupae in underground diapause because a few butterflies were on the wing the following spring, and the host plant recovered as Indigofera often does after a severe fire – but the ants’ nests in the Candlewoods had gone. LepSoc Africa members are keeping a vigil, and a reward has been offered to anyone discovering a new colony, but the outlook is bleak. Its current IUCN status is CR A2; B1ab(iii,v)+2ab(iii,v); C1+2a(i,ii); D, which is about as far as one can go before reaching CR (PE) – Critically Endangered, Probably Extinct.
So, what does it all mean?
Ultimately, migration and dispersal are all survival mechanisms tuned to an organism’s ecological needs and habits. Such behaviour is exhibited by vertebrates and invertebrates, and plants (over a long enough time frame). Time frames are important. Most vertebrates live long enough for migratory pathways to become habitual, if sometimes aided by the ability to sense the earth’s magnetic field. Invertebrates don’t live long enough to learn a migratory path. They must rely on their senses as well, but much of this behaviour must be instinctive – hard baked into their genetic makeup because one generation cannot learn from the previous one over a multigenerational migration. Factors such as wind strength and direction, changes in humidity, diurnal/nocturnal length (and rate of changes in this), host plant presence and abundance (or lack thereof), predator satiation, and senses we cannot experience ourselves such as magnetic field awareness, must all play a part.
Often, migratory behaviour is replaced by sedentary behaviour. This may be seasonal, as in Danaus plexippus, or driven by stranding in areas that cannot support onward migration. It may lead to speciation due to genetic drift, further dispersal under different circumstances, or extinction. The latter must occur almost at the same rate as speciation, to maintain a biodiversity equilibrium. The spectrum between the two extremes must be very complex and will have undergone many changes over the hundreds of millions of years today’s migratory palimpsest has taken to be written.
Steve Woodhall is a butterfly enthusiast and photographer who began watching and collecting butterflies at an early age. He was President of the Lepidopterists’ Society of Africa for eight years, and has contributed to and authored several books, including Field Guide to Butterflies of South Africa and Gardening for Butterflies. His app, Woodhall’s Butterflies of South Africa, is described as the definitive butterfly ID guide for South Africa.