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January 2005



On the trail of missing Mopane Worms

Rob Toms and Mashudu Thagwana


 "Mopane Worm" feeding 

From a cultural point of view the "Mopane Worm", also known as Masonja in North Sotho, is one of the most important insects in Africa. Harvesting of the protein rich larvae for food is a lucrative, multimillion Rand industry. Researchers however find that in some areas the Masonja industry may be in trouble. Rob Toms and Mashudu Thagwana of the Transvaal Museum went in search of the answers.

The Masonja's most important food plant is the Mopane tree Colophospermum mopane, meaning that to a large extent the conservation of the insect depends on the conservation of the tree. Monitoring these trees gives a good indication of the state of the Masonja populations.

Every year there may be two harvests, which can potentially yield millions of kilograms of larvae worth millions of Rands. The first harvest is in December and the second harvest coincides with Easter at the end of March or beginning of April.

In the Veld

In April 2004 Rob Toms and his team investigated the harvesting of Masonja in the field. A quick survey driving through the Mopane Veld revealed huge differences in the level of defoliation in different areas. West of Tshipese and on the N1 up to Musina and West to Alldays there was about 90% defoliation, but East of Tshipese towards Pafuri Gate there was only about 0.01% defoliation. Defoliation indicates a thriving Masonja population.

Defoliation of trees by the Mopane Worm

The strong contrast between the good Masonja crop West of Tshipese and the poor crop East of Tshipese is readily explained. On the N1 up to Musina and West to Alldays there are several game farms, some of which accommodate lion populations. Harvesting of Masonja on some of these farms is negligible, so they act as great Masonja reserves where the species is safeguarded. If over-harvesting occurs, recolonisation by the populations on the nearby reserves may occur within a few seasons. 

For example, one of the farms visited had a relatively small crop in December 2003, forcing the owners to place an embargo on harvesting to allow the population to recover. The recovery was so successful that up to 1000 pickers per day were operating on the farm at the end of March the following year. Excellent crops were also reported in the Mapungubwe National Park. Here Bernard van Lente reported that "during April 2004 they had what could only be described as an outbreak". 90% of all mopane trees in the Limpopo valley were stripped of all their leaves. In the park the trees recovered readily having sprouted new leaves by mid-April, due to good soil moisture.

In contrast to this, much of the area between Tshipese and Pafuri Gate is inhabited by people who regard Masonja as communal property available for anyone and there are few reserves. Here Toms and team believe that over-harvesting during previous seasons contributed to a small crop in April 2004 and that over-harvesting of this crop meant that the following crop would also be small, even if environmental conditions are optimal.

Environmental factors

But this argument may not hold true for areas such as the Kruger National Park. Toms believed that the poor Mopane Worm crop in this protected area was not due to over-harvesting. For more information regarding the situation inside Kruger National Park, a report was obtained from Johann Oelofse at the Mopane camp. He reported that "judging by the number of mopane worm moths, present during late 2003, we expected an "all time bumper crop" of mopane worms during the November/December season and indeed large numbers of small caterpillars were observed soon after hatching. Lack of rain and a blistering hot sun with accompanying very high day temperatures however physically "frizzled" these little guys (all approx 25mm to 30mm in length) and their dried out remains were seen lying thickly under mopane trees and shrubs. Only here and there were small pockets of fully developed worms observed. Although abundant rains and milder temperatures followed between January and March, the usual March/April "second appearance" of mopane worms just did not "happen" at all". These observations show that even with minimal harvesting in a protected area, there may be a crop failure induced by adverse environmental conditions. However, it also seems probable that circumstances may exist where a crop failure under nearly optimal environmental conditions may be induced by over-harvesting.

Where Masonja reserves exist the species is safeguarded from over-harvesting so there is no reason to regard this as an endangered insect. However, there may be areas of local extinction which are far from viable populations and where successful recolonisation may be unlikely because of human intervention, unless community participation is negotiated. The strong contrast between the good crop in the West and the poor crops in the East is most interesting. Environmental conditions can apparently play an over-riding role but over-harvesting could be an important factor in some areas.

Myths and over-harvesting

 Harvesting the Mopane Worm can be a lucrative industry

In the case of the mopane worm in South Africa, one of the primary causes of over-harvesting appears to be based on myths in which there is "no such thing as a life cycle" and indeed no understanding thereof. According to one myth, it is believed that when the mopane worm leaves the tree and buries itself in the ground prior to pupation, it is going to die. If the worms were really all going to die, there would be no reason to restrict the harvest. Another myth enforces the belief that the moths of the mopane worm go into hibernation after they have laid the eggs, so in this case the reappearance of the moths is in no way linked to the harvesting or over-harvesting of the larvae.

However, myths do not always prevail. Different people have different indigenous knowledge, so solutions to these problems can also be found within indigenous knowledge systems and many people do understand the life cycle of the mopane worm and the implications for sustainable harvesting. For example, in some areas traditional leaders place an embargo on the harvesting of larvae before or after a certain date. An embargo at the beginning of the season should prevent the over exploitation of small larvae, which is a wasteful practice. It may take up to 50 small larvae to make a meal for one person while 5 large larvae might suffice. The harvesting of small larvae is wasteful and should be strongly discouraged. At the end of the season, their restrictions on the harvesting of mature larvae allow some of the larvae to complete the life cycle, thus safeguarding the crop for the next season.

Rob Toms believes that sustainable harvesting is the key to increased production. "With sustainable harvesting we believe that there can be a dramatic increase in the value of the harvest of certain edible insects. When the rainy season starts the Mopane Moths will emerge to lay their eggs and a new Masonja crop will start. If we have good rain in December there can be a good crop in some areas. However, in any area where the numbers are low it would be advisable to restrict the harvest and allow most of the Masonja to complete their life cycle to build up the population for the next season in March 2005". The problem is putting this into practise. Toms believes that further education is the key and as a starting point has produced descriptive posters on the life cycle of this valuable insect for distribution.

More information:

Posters of the Mopane Worm life cycle are available from Transvaal Museum shop.

For more information please contact: Dr Rob Toms at the Transvaal Museum, South Africa - 

Photos supplied by Rob Toms

Related articles:

The Mopane Worm - Indigenous Knowledge in the Classroom

Eat Your Bugs! (Edible Stinkbugs)


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