It was mentioned that after my last article, readers wanted to know more about butterflies that live with ants. Or more broadly, non-plant feeding lepidoptera!
This kind of behaviour is widespread; butterflies (and moths) are not all cute little herbivores like everyone thinks they are. The association of Lycaenidae, or ‘gossamer-winged’ butterflies with ants probably goes back 50 – 60 million years, when the family split from the main ‘butterfly’ lineage – as DNA studies tell us. By then, ants had already been on the scene for around 100 million years. Many ants are predators, as are most insects if it comes to that.
The world has undergone massive changes since then, and butterflies have been scattered all over the globe by continental drift. We find ant associated Lycaenidae all over the world. Europe has them – in fact the behaviour was first discovered in England at the beginning of the 20th century. America has them too. They are everywhere!
In Africa, the phenomenon has been accelerated by the uplift and aridification of our continent over the past 10 – 30 million years. This made the vegetation change from forest to savanna, and then grassland. Later, the karoo, desert, and most recently, fynbos biomes developed. The climate became colder and more seasonal. It’s not only insects that were affected. It’s what drove the evolution of today’s herbivores, and a certain ape that adapted to living on the ground…..
But I digress. If there’s no vegetation around for a long period of the year, either because frost kills it or fires burn it, what are insects to do? One option is to become a carnivore and live underground. And many have done this over the epochs. But there are other feeding strategies that go back further into the past.
Scale Insects (Homoptera) are a type of bug, that like the ants has an ancient lineage. Ants are well known to ‘milk’ bugs for their honeydew which is the waste from plant sap they suck. ‘Buffs’ are found all over tropical Africa, especially in the equatorial forests, where there can be dozens of related species in one clearing. There are plenty of them in forests like the ones at Lekgalameetse. They don’t only drink bug honeydew – extra-floral nectaries on trees or herbaceous plants also attract them. This kind of thing was probably happening long before flowering plants evolved.
Here we see another species of buff, also sucking Homopteran honeydew, but this time in the company of some Crematogaster (cocktail) ants. It’s likely that this is how deeper, more complicated ant associations evolved, but with these butterflies (subfamily Poritiinae) the association is with the adults. The caterpillars feed on lichens, another association that probably pre-dates plant eating. Lichens evolved a long time before vascular plants did. There are, however, lots of examples of plant-eating caterpillars that live with ants.
The butterfly genus Lepidochrysops (giant cupids), with 137 described species in Africa, is found in a wide variety of habitats. The northernmost species are found in savanna grasslands in equatorial Africa, and the southernmost in the fynbos of the Cape. DNA evidence has shown us that they evolved from the closely related Euchrysops (smoky blues), most likely when Africa was transitioning from mostly forest to a savanna mosaic.
Euchrysops are widespread in Africa; they are not restricted to grasslands although many of them are found in such habitat. At least one species has adapted to living underground as a caterpillar, and they are all ant associated, but they don’t predate on the ants like Lepidochrysops caterpillars do. They are myrmecoxenous, which means they are attended by ants, but the ants do nothing to harm them. Like many of the Lycaenidae the caterpillars probably use chemicals (pheromones) to influence or control ant behaviour. They have another trick – many of them exude honeydew from a gland on their back near the tail end. This, like the honeydew from scale insects, attracts ants to them.
This Sabi smoky blue is nectaring on Ocimum obovatum, along with a sugar ant, Camponotus sp. The same ant/plant combination is found in the Lepidochrysops, but with those the ants are prey, not partners!
This is one of Africa’s rarest butterflies, at present only known from The Downs at Lekgalameetse. The egg will hatch into a caterpillar that will eat the ovaries of the flower. When half grown it will exude pheromones that control ants’ behaviour, so that they carry it into their nests and allow it to feed on their brood. Those nests are usually underground, so the caterpillars are protected from the fires that often burn when the grasslands are dry. This is known as phytopredaceous behaviour – they begin on plants (hence phyto) and switch to predation on ants.
Giant cupids are among the largest and most spectacular of the ‘blues’. This brilliant giant cupid is a species that can be found from the KwaZulu-Natal Midlands grasslands to the fynbos of the eastern Cape. Its wingspan is up to 40mm, making it a conspicuous sight as it flashes across the veld. These are in the subfamily Polyommatinae. Many of these are myrmecoxenous but phytopredaceous behaviour has only evolved twice. Once in the Lepidochrysops, and once in the distantly related and rare Eurasian genus Phengaris (the English ‘large blue’).
Ant association is taken to its extremes by other subfamilies of the Lycaenidae. We saw the Miletinae (skollies and woolly legs) in the last article, but the most widespread examples are in another subfamily, the Aphnaeinae. These are ‘Africa-centric’, but examples are found in Eurasia. The opals (genus Chrysoritis) are unique to South Africa and form two distinct ‘clades’. The ‘eastern clade’ are coppery butterflies found in shrub patches along the eastern mountains and coast where the caterpillars feed on Ebenaceae (e.g., Diospyros sp.). Mooi River opal, Chrysoritis lycegenes, is typical of these. Other, similar, species are found in Mpumalanga and just penetrate Limpopo. The caterpillars have lots of adaptations to bind ants to them. This Mooi River opal caterpillar has three ways to control ants. At its rear (top of the photo) it has a honey gland and two ‘tubercles’ (the white structures on the side of its body) exude pheromones that control the ants. All over its skin it has tiny glands that exude different pheromones. It’s basically a little walking chemical warfare agent!
The ‘western clade’ of Chrysoritis is found in the fynbos and karoo biomes from Lesotho, westwards. It has some of the most spectacular small butterflies in the world. This Uranus opal, photographed high in the Western Cape mountains, is an example of this, but there are several other species. This clade is thought to be evolving as we study them, because they inhabit tiny ecological niches that shift as the climate changes, and many of them are incredibly difficult to tell apart! The caterpillars use a wide range of plants, but most of them use Thesium (Santalaceae).
Hutchinson’s highflier, covered in an earlier article, is another member of the Aphnaeinae. That genus is found all over tropical Africa; some species are found in the wet equatorial forests of central and west Africa.
The genus Cigaritis is found not only in Africa but in southern Europe and in Asia as far east as Japan. There are five species in South Africa. They are also gorgeous little butterflies, the caterpillars closely resemble those of opals, and like those, shelter in cocktail ants’ nests, and feed on a wide range of plants. Cigaritis are found in a wide range of habitats from succulent Karoo and desert in southern Africa, savanna and forest across tropical Africa and Asia, and desert again in north Africa and Arabia.
Despite this wide range, they most likely evolved in southern Africa as it was aridifying, then spread further afield as climate change caused their preferred habitat to expand and contract with time.
They are among the most evolutionarily advanced butterflies and are fascinating as well as beautiful.
