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Protecting the dwindling 'diamonds of Bobirwa'

Every summer, in step with the season's rains, the mopane woodlands of eastern Botswana come alive with caterpillars that people have harvested for centuries. But mopane 'worm' numbers have dwindled here in the past decade, as rains come less predictably, and more people lean on this over-harvested insect for food and income. How the Botswana government responds to the population crash of this important livelihood source for its people can have lessons for other southern African countries, as the region becomes hotter and drier, and people’s livelihoods are threatened, writes LEONIE JOUBERT *.

When the summer rains come to the eastern parts of Botswana, people travel into the region from hours away, and head into the mopane woodlands in search of the ‘diamonds of Bobirwa’. The caterpillars of the region’s distinctive emperor butterfly break from their eggs in time with the rains, and explode in a feeding frenzy on the leaves of the mopane trees. That’s when people gather them up by the bucket-load, and take them back home either to use as food for themselves, or to sell at the local market.

For generations, people have dried the caterpillars, and either cooked them into a relish, or ground them down to powder and mixed this into porridge or yoghurt. Some people even travel from as far away as South Africa, coming here when the caterpillars flush to buy the dried insects for use in cattle feed: they mix the powdered mopane ‘worms’ into sorghum meal with a bit of salt to feed to their livestock.

It’s an important source of protein and income for the people of Bobirwa.

But mopane ‘worm’ numbers have dwindled in recent years, explains local ecologist Ephias Mugari, in part because of extended periods of drought, but also because of greater pressure on the resource from a growing number of people who rely on it as a food and income source.

He recommends that the Botswana government should consider reviewing the permitting and monitoring conditions that govern how people harvest the insects each year, if they are to stop the insect population from declining even further. Government might even consider closing the harvesting season for two or three years to allow the resource to recover.

Mugari, a doctoral researcher at the University of Botswana, has visited the Bobirwa district several times since starting his research there in February 2016. His aim is to gauge the extent to which the local people depend on various ecosystems for wild sources of food and medicine, or fodder for their animals, and understand how rising global temperatures and shifting climate are impacting on the availability of these natural resources.

“Botswana is one of the sub-Saharan countries that’s most vulnerable to climate change, for various reasons. I visited this specific area to establish all the important ecosystem services that people in Bobirwa rely on, especially those that are linked with the state of natural vegetation and are therefore responsive to climate,” he explains.

“Mopane caterpillars, what we call ‘phane’ in Botswana, are a key part of these ecosystem services. They’re an important source of protein and income, and the health of the mopane caterpillar population depends on the condition of the mopane woodlands, which are affected by rainfall.”

Mugari visited some 10 villages in the sub-district throughout his research. When he returned to the region this February, the rains were late again. The mopane caterpillars usually flush with the rains in December, and again in April. Farmers also time their crop planting with the rains. But even by the height of the summer, Mugari found that many of the farmers in the region had not planted any crops yet, in response to this lack of rain.

Botswana: getting hotter and drier

Botswana’s distance from the cooling effects of the nearest oceans, or humid tropical forests is one of the reasons it is expected to warm faster than many other countries, as atmospheric carbon dioxide rises.

The landlocked country is already vulnerable to climate change, with higher temperatures and longer, more severe droughts becoming the ‘new normal’, according to Tiro Nkemelang, a climate scientist at the Botswana Institute of Technology Research and Innovation (BITRI).

“Global temperature warming is already set to exceed 1.5°C above pre-industrial levels, but Botswana will cross that threshold much earlier because of its semi-arid climate,” he says.

According to a recent climate modelling study done by the African Climate and Development Initiative (ACDI), based at the University of Cape Town in South Africa, researchers found that this 1.5°C average increase could occur as early as 2024.

“The climate modelling suggests that

with a 1.5°C increase in temperature here, Botswana will see greater temperature-related extremes: more heat waves, more warmer days, and fewer cooler days,” says Nkemelang, who conducted some of this modelling while studying at the ACDI.

Periods of drought are expected to last longer, with fewer rainfall events breaking them, according to Nkemelang’s modelling, but when the rain events do come, they are likely to be more intense, resulting in flooding. The overall climate trend will be one that is hotter and drier.

Because people in semi-desert countries like Botswana are dependent on rain-fed agriculture, longer, more severe droughts with shortened and less predictable rain seasons will have significant impact on crop yields and food availability.

Communities like those visited by Mugari in Bobirwa generally have a low asset base, so are highly dependent on the natural environment for resources: food for themselves, fodder for livestock, fuel and building materials, water, and so forth. The case of the mopane woodlands and its caterpillars in eastern Botswana, shows how dependent so many in semi-desert parts of southern Africa are on healthy ecosystems.

“When I questioned the villagers in the Bobirwa district about their experience of harvesting mopane caterpillars over the past decade or so, most said there had been a significant decrease in the insect’s abundance. They also said that the caterpillars’ flushes were inconsistent, that one season they’d appear near one village but not another.”

He said the locals saw a clear link between declining caterpillar numbers, and ongoing drought in the region.

But he also found clear signs that growing demand for the resource was putting unsustainable levels of harvesting pressure on the insects.

“If people want to harvest mopane caterpillars in Botswana, they are required to have a permit from the State. But the permit only costs two pula - that’s about US$ 0.20. And there is no monitoring of harvesting. People just travel out into the woodlands and collect whatever they want,” says Mugari. “They’re also digging up the pupae buried in the ground towards the end of the harvesting period.”

Even though this food source is known colloquially as the mopane ‘worm’, it’s not actually a worm, explains Mugari. A worm is a type of animal, like an earthworm. This mopane ‘caterpillar’ is the juvenile life stage of an emperor butterfly species, the Imbrasia belina.

In the case of this butterfly species, the adults lay their eggs on the leaves of the mopane trees usually twice during the rainy season. The eggs hatch, leaving caterpillars to feed on the leaves and grow rapidly.

Once they’ve completed this part of their life cycle, the caterpillars crawl down to ground level, bury themselves in the soil where they go into pupae phase, and will stay there for several months, until the next rains come. Emerging as butterflies, and unable to eat, these insects only have about four days in which to mate and lay eggs, before they die.

If people dig up the pupae, they’re taking away from next season’s breeding stock, says Mugari.


How should the Botswana government respond, to address this population crash?

“The State can’t do anything about adverse climate change,” says Mugari, “but it should consider working with traditional leaders and local authorities to monitor and enforce permitting conditions more strictly. They might also consider banning mopane caterpillar harvesting for two or three seasons, to allow the population to complete a few breeding seasons, and bounce back.” But key to supporting the communities that depend on the mopanes is to ensure that they have other ways to make a living or survive off the land. If there aren’t phane to harvest, people need to have alternative livelihood options to rely on, researchers say.

*Leonie Joubert is a South African science writer and author. This article was funded by ASSAR (Adaptation at Scale in Semi-Arid Regions), a research consortium looking at climate change in semi-arid parts of Africa and India. The article is the first of a six-part series Mmegi will be running


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