Has there been a temporary expansion of the Savannah (or African) honeybee into the territory of the Cape honeybee? Words and images by Geoff Tribe and A. David Marais.
View of the farm where these observations were made about 35km from Touwsrivier.
The Cape honeybee (Apis mellifera capensis) is restricted to the winter rainfall region of southern Africa but is purported to have an interface with the Savannah bee (Apis mellifera scutellata) along the margins of this region which has been designated as the ‘hybrid zone’.
Because the outer margins where the two honeybee races converge are mostly semi-desert, it has been postulated that the low numbers of wild colonies and the correspondingly reduced population pressure between the two sub-species, could result in co-existence.
Several factors may influence the habitation and cohabitation of the bees.
The area where the highest numbers of ovarioles occur in laying-workers of the Cape bee is regarded as the ‘heart’ of the capensis distribution. This lies in an inverted triangle that can be drawn from Stellenbosch in the west, to Swellendam in the east, and to Cape Agulhas in the south.
The Cape bee has maintained its dominance in the winter rainfall regions for many thousands of years despite scutellata hives being brought into their region. Within a few years such hives become capensis because capensis workers find their way into scutellata colonies and become laying-workers and eventually take over these colonies by becoming pseudo-queens. This is due to the higher level of queen pheromone possessed by the Cape bees.
The search for honeybees on a farm in the Tanqua Karoo 35km north-east of Touwsrivier has only yielded capensis bees on it for the last 20 years of occupation. The identity of the bees has not been determined scientifically by dissection but having worked with both races for many years it is possible to superficially identify the two races with some certainty.
Apis mellifera capensis visiting a Mesembryanthemaceae flower.
Four colonies of bees were located on the farm, two in aardvark burrows and two in crevices in shale outcrops. There were, however, indications that there were more colonies, but the farm was not explored in great detail. All four colonies absconded during the recent eight-year drought. The annual rainfall over the past decade averaged 102mm with a range of 34 to 226mm. With the exception of 2018, the preceding 5 years had rainfalls of less than 90mm per year. Generally, the rainfall during November and December was <10% of the annual rainfall but in 2021 it was 26mm (37%).
This drought was broken by recurrent episodes of significant rainfall from November 2022 to May 2023 which were unprecedented for the last 20 years. The rainfall of 143 mm in December resulted in a flood. Indeed, the Tanqua Karoo and adjacent regions experienced widespread floods. Dry river streams turned into raging torrents and the sand was washed down from the hills onto the plain below, leaving a wide riverbed with solid shale bedrock.
Over the six months of increased rainfall, the growth of the vygies in particular was particularly good. Whereas one could easily walk in the empty patches between the vygies, they now coalesced. Vachellia karroo (‘soetdoring’) immediately responds to substantial rainfall and within a short while these trees flowered twice in succession and became an attraction for all manner of insects from beetles, wasps, flies, caterpillars, butterflies, bugs, aphids, and solitary bees … but no honeybees were seen. Presumably the Cape honeybees that were observed collecting water at various seepages throughout the farm were visiting alternative sources which were more profitable. The flowers develop only on the young growth of that season and so growth, dependent on rainfall, precedes flowering by four to five weeks.
Due to the floods, the Vachellia karroo and Searsia burchellii trees which were scattered along the rivulets had their roots exposed. The roots had been unable to penetrate the shale bedrock but instead had followed along the banks of the river, some being as long as perhaps 12 metres. In most cases it appeared that the combined mass of the roots of a tree was greater than that part above the soil. Another observation was that many of the larger succulent species such as Tylecodon paniculatus and Tylecodon wallichii had rotted and collapsed due to the perpetually soaked soil.
Apis mellifera scutellata visiting the flowers of Eberlanzia ferox.
In May 2023 on one of the hills where the vygie Eberlanzia ferox was flowering, were found some bright yellow honeybees with little pubescence on their abdomens which could only be scutellate. Had they temporarily expanded into capensis territory due to the excessive (summer) rains and the resulting mass flowering of plants which could facilitate such an expansion? Perhaps the history of the region should give an indication.
The farm is situated in the Tanqua Karoo, the name probably being derived from “Sanqua” who were the first inhabitants of the region. It is also known as the ’Onder Karoo’ and ‘Ceres Karoo’. The Khoi subsequently moved into this area with their stock and the competition for pasture and water resources became intense. This was before the days of the wind pumps and the extraction of subterranean water.
The Trekboers then expanded into the interior in large numbers in the 18th century. In the 1800s this was a contested area which existed between Touwsrivier in the south, to the Hantam Mountains in the north and the Roggeveld escarpment inland. It was only possible to farm small stock in this area if a farmer was able to move across the boundaries between the winter and summer rainfall area in different seasons – which still is pertinent today.
Farmers still take their sheep down to the Tanqua Karoo in winter to escape the extreme cold of the escarpment. The demarcation between winter and summer rainfall regions is not a precise line but rather a shifting corridor in which there might be little rainfall in both the winter and summer months. This all-season rainfall corridor coincides roughly with the line of the interior escarpment. Sheep and goats could survive in the winter rainfall region during winter but could not remain there when it dried out and the heat became intense. They would be moved further inland onto the higher escarpment in summer.
This region was subject to cycles of excessive rain followed by drought which resulted in competition for grazing amongst the Trekboers, Khoi and San hunters. This became an area of continual conflict for about a century. An example of this conflict is a report by Field Sergeant Charl Marais in September 1779. Although a comprehensive record does not exist for the climate, flora and fauna, some information is available about the rainfall in the region.
Historically, the years 1700 to 1704 were years of poor rainfall that was followed by normal rainfall in 1705. Heavy rains in 1706 caused a great loss of livestock. July 1715 was exceptionally cold and wet and was associated also with an unknown cattle disease which led to high mortality. A severe drought in 1800 was followed by substantial rainfall in the Roggeveld in 1803 with many flowing streams. But during 1805 an extreme drought was experienced in the Tanqua Karoo. In contrast, there is a record that in one year the summer rains were so widespread that they swept through the Karoo to the sea.
The emerald fruit beetle Rhabdotis semipunctata on Vachellia karroo flowers.
Visiting this farm regularly throughout the years, the effect of the climate and weather on the ecology of the area has become clearer. Nothing stays the same from year to year. An insect species which is prolific one year may disappear totally for a number of years before reappearing again when conditions are suitable. A good example is the emerald fruit beetle (Rhabdotis semipunctata) which is found cavorting on the flowers of Vachellia karroo. Prior to the long drought they had been prolific but disappeared, only to re-appear when V. karroo flowered again due to the heavy rains in 2022/3.
Botanists visiting the farm over a weekend were able to identify 98 species of plants – and many more have yet to be identified. Yet honeybees are rarely seen on flowers despite hours of hiking each day on the farm. However, they are desperate for water in the hot summer months and will visit artificial pools of water. Despite masses of vygies of various species flowering in spring, it is rare to see a single honeybee visiting them. It appears that the amount of forage in the worst month greatly influences the carrying capacity of wild colonies in an area. Honeybees have been observed visiting Haemanthus coccineus, Brunsvigia bosmaniae and various species of Asteraceae.
Many species of succulent plants appear to have niche pollinators, many of them solitary or sub-social bee species. Tylecodon wallichii produces an exceedingly long raceme which towers above the karroid scrub. It attracts a Xylocopidae (carpenter bee) species which flies from the one exposed flower stalk to the next which is clearly visible in the landscape as they project well above the karroid scrub.
There are also seven species of carrion flowers (Stapeliads) whose flowers produce a stench of either sweat, urine, faeces or a rotting cadaver by which they attract flies which pollinate them. This makes at least a subset of plants independent of bees for pollination. The pollination of these plants is further amplified by the placing of all the pollen in a sac (pollinium) which the fertilising insect transfers. A similar strategy is employed by orchids, of which only one species has been found on the farm.
Occupation of the region by humans has undoubtedly affected the ecology of the region; especially with continual occupation and the introduction of livestock. The farm has not had stock on it for 20 years (except occasionally those of the neighbours which find an opening in the fence) but there are resident rhebok, duiker, steenbok and three pairs of klipspringers. Baboons regularly pass through and leave a tell-tale of the chewed roots of Euphorbia rhombifolia.
Game abounded in this region before firearms appeared. Colonel Robert Jacob Gordon in 1777 attested to the large number of lions in the Tanqua Karoo. Augusta de Mist (1803) also commented on the large numbers of lions, leopards and hyenas and was enthralled to see a flock of about 300 ostriches on the southern plain below the Rooiberg which forms the one boundary of the farm. The Bokkeveld in fact was named after the scattered herds of springbok which migrated from the interior into this territory at times. The only accommodation on the farm is an old ‘skeerhok’ in which to sleep from which a beautiful view over the veld can be seen as the sun sets.
Apis mellifera capensis collecting water in summer on the farm.
There is no doubt that weather and climate have a large effect on honeybees which expand in strength and number of colonies in favourable years. During unfavourable times, the honeybees decrease in numbers and possibly abscond. Judging from trap boxes placed out each year in the Swartland, drought can drastically curtail the numbers of migrating reproductive swarms. The banded bee pirate, Palarus latifrons, occurs on the farm and there are also generalist arthropod predators such as the Asilidae robber-fly. However, although honey badgers have a wide distribution across Africa they have not been observed on the farm.
The interesting observations over approximately two decades need further study before the extensive development of facilities to generate electricity by harnessing wind or sunlight overwhelm the area. The Perdekraal Oos wind farm is located within 10 km of the farm where the observations have been made.
The environmental impact studies for this development and other developments under consideration in the region, reflect relatively short periods of study and do not provide detailed information on the waxing and waning of the numbers of bees and their nests, the interaction of the capensis and scutellata bees as well as other related pollinators. It is likely that periods of more summer rain have temporarily favoured scutellata bees while the capensis bees can be viewed as the predominant inhabitants of this region.