Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours. . . but actually many media including 'digital' paintings with the computer!"
I've written about the Mopane Tree before, in which article I mentioned the nice, fat, juicy caterpillars that feed on them – and on which people feed too – and there's a picture of one on my father's hand in there also. But the caterpillars, and also the moths that they turn into, deserve an entry of their own! This moth, Gonimbrasia belina (or sometimes classified as Imbrasia), is actually one of the handsomest and largest ones to be found in South Africa.
Mopane moths belong to the Saturniidae, the Emperor Moth family. As you might expect these are often large and spectacularly handsome moths. The largest moth in the world – indeed the insect with the largest wing surface of any living today – is the Atlas Moth of Southeast Asia, with a wingspan of up to 28 cm/11", which is also a member of this family. The emperor moths occur all over the world but are most diverse in tropical rainforests.
The Mopane moth, however, does not live in rainforests, ranging over the entirety of South Africa (and also into our neighbor countries and through southern-central to Eastern Africa as far as Ethiopia, and apparently also Senegal) and favouring dry, open regions such as semi-desert, grassland or dry woodland. It is not at all restricted to Mopane woodland. This dry woodland type only occurs in the far north of South Africa. While the caterpillars are associated with Mopane trees and shrubs, they also feed on a very wide range of other plant species, mostly trees growing in savannahs.
These moths are not quite as large as the Atlas moths, but still very large, having a wingspan of 12-15 cm/5-6". They can be recognized by their wing decoration: plain, fairly straight black-and-white bands over the fore and hind wings, small eyespots on the forewings, and large eyespots on the hindwing. The wing ground colour can vary from greenish or brownish to reddish. The eye spots alone are not characteristic: similar eye spots are found in a vast variety of other butterfly and moth species, especially in the emperor moth family. The idea used to be that the eye spots make the moths look like much larger, fiercer creatures, and so could scare away predators. There seems to be no actual proof of this, though. A recent study concluded that indeed the eye spots do deter predators, but not because they look like eyes. Other highly conspicuous, brightly coloured shapes and patterns also scared off predators. The conclusion was that the factor deterring the predators was 'visual loudness' … a startling, visible signal that might affect many predators almost like a sudden loud, irritating noise can startle a human. Alternatively, predators may actually target the eyespots, pecking at the wings and so missing the more important head and thorax region of the moth. As well as these protective functions, the eye spots may simply be attractive to their fellow moths!
Life of a Caterpillar
Like other moths, these start their lives as caterpillars. The caterpillar is in fact the most significant part of the moth's life in terms of overall time (unless you count the pupa – but that is a sort of inert existence, being nothing more than a packaged broth of liquefied tissues). Caterpillars are often seen as nothing more than 'eating-machines': a food-processing bag of a body with a mouth at one end and feet to carry it from one food source to the next. I've often wondered if we shouldn't give caterpillars more credit. I've had lots of a great variety of different kinds in my garden and have spent a lot of time watching them. They are responsive in a variety of ways and have skills we often don't properly appreciate, one of which is finding food plants. While the moths often lay their eggs right on the leaves of the right kind of food plants, caterpillars can be removed and taken away from these but will find their way back if allowed, and if one bunch of caterpillars completely defoliate one plant they will seek out and find others of the right species. Sometimes the closest suitable plant could be quite a distance away but they still find them, and that while crawling on their bellies on their stubbly little legs. We still don't know just how they find their food – do they seek them out using vision or smell? Perhaps both, but still, that means the caterpillars do possess sophisticated sensory equipment, because in typical habitats there are hundreds of species of plants growing together, only a specific one or few of which are suitable food.
Mopane moths lay their eggs in the summer, when the first rains of the season are already well underway and the Mopane trees (and others) have erupted in new, fresh, green leaves. Upon hatching the caterpillars are quite small, and pass through four moults to reach their ultimate size. It is the final larval stage which is the most sought-after by humans. As you can see in my photo in the Mopane entry, they are quite large, commonly exceeding 10 cm/4" in length. They have a spiky appearance but these spikes don't sting and burn as some of the spikes and hairs in other caterpillars do. The caterpillars grow very rapidly and while they may completely defoliate mopane bushes and trees, they reach the end of their moult cycle fairly quickly, giving the plants a time to recover and sprout new fresh leaves.
If the caterpillars survive after their final moult, they will descend and burrow into the soil, where they will turn into pupae. These pupae will stay in the soil all through the autumn and winter, while inside the new moth slowly assembles. Then come the next summer the moths will emerge, breed and lay eggs, in time for the new crop of Mopane leaves. The moths live for only three or four days and die soon after breeding.
Mopane eggs are susceptible to fungal infections, while the caterpillars can succumb to a virus disease. They are also preyed upon by birds and other animals, including us humans!
A crunchy, tasty snack?
Mopane worms are harvested in large numbers in northern South Africa as well as other African countries. It is often women and children who hand-pick them off trees and bushes. They might look very unappetizing … actually they are not at all nice tasting … I've tried them once, and only once. But they are very nutritious, about 60% protein by weight, with a significant fat content as well. As such in rural areas they form a significant addition to the sparse regular diets of many people. To prepare them for being eaten, their innards first need to be removed, the details of which I'll spare you. Next they are usually dried in the sun, or smoked (as in, suspended over a fire so the smoke can permeate them). They can also be pickled in brine. This is done on an industrial scale in South Africa, the product being canned, often with tomato or chili sauce, and available in shops and supermarkets in many places.
The dried worms can be eaten just like that. Sometimes they are soaked in water to rehydrate them, and then fried to a crisp. They can also be cooked with vegetables as a stew and served with maize porridge. Read more about this interesting taste experience here
As hard as Europeans and Americans may find it to believe, these worms are popular enough to be a significant industry in southern Africa. Botswana and South Africa export them in large quantities – South Africa is estimated to trade in about 1600 tonnes of them each year! In terms of farming economics, these worms are three times more efficient at turning leaves into protein than cattle are. But actually farming them may not be a good idea. They occur in abundance on 'wild land' where they have been regarded as not belonging to any landowners, people of the entire community being free to harvest and eat them or sell them cheaply at local markets. When farmers lay claim to them and their habitat, and often ask people to pay for the privilege of coming in to harvest them, it actually causes difficulties for the rural people who used to have free access to them. And having wild worms available for free means that in many areas it is difficult for farmers to enter the market and sell the worms at worthwhile prices. Also, with the incentive of making money, the worms end up being overharvested in the wild, reducing yearly yields. On the other hand, game farmers sometimes combat the caterpillars with poisons because they believe they are undesirable competition for food with the farmers' game. Actually the competition is not very significant because of the caterpillars' short life cycle I described, after which the trees sprout new fresh and juicy leaves which are actually very popular with browsing game.