By: Karin Sternberg with inputs from Sue Milton. All images were taken by the author.
Karin Sternberg is an amateur naturalist and conservationist focused on the study of solitary bees and wild honeybees in the Great Karoo region. Over the past decade, she has conducted research into the ecologies of these essential pollinators, documenting more than one hundred wild honeybee nests during the course of her fieldwork. Her research is self-funded. Sue Milton is an arid zone restoration ecologist based in the Karoo region of South Africa. She is the owner of Wolwekraal Nature Reserve and Wolwekraal Conservation and Research Organisation (https://www.wcro.co.za) that promotes conservation, education and research in the Karoo.
There are 2755 bee species in sub-Saharan Africa, about 1300 of which occur in South Africa. Of these, only the honeybee and 10 species of mopane bees store honey, but all bees are important pollinators of a wide variety of plant species. They pollinate not only fruit and field crops, but most of the annuals, succulents and shrubs that make up the natural grazing lands, particularly in the more arid parts of South Africa. The arid, winter-rainfall region of South Africa known as the Succulent Karoo, is extraordinarily rich in succulent plants—and in the solitary bees that visit their flowers. Bee hotspots with around 700 bee species are found in the arid winter and aseasonal rainfall regions of South Africa.
Nesting sites of the solitary bees Samba (left) and Colletes (right) on the inner edge of an aardvark burrow.
In September 2024, I spent several weeks documenting the diversity and behaviour of solitary bees on Wolwekraal Nature Reserve which lies within the arid, aseasonal rainfall bee hotspot in the southern Karoo. This Nature Reserve protects rare succulent plants, most of which are pollinated by bees and flies, but the reserve is also used for conducting restoration trials. Most of these focus on revegetating patches of bare ground where over-grazing or corralling destroyed vegetation centuries ago and led to wind-blown loss of the shallow topsoil. Over millennia the vegetation here has adapted to withstand dramatic temperature fluctuations, from severe winter frosts to scorching summer heat at times exceeding 45°C, often enduring prolonged periods of drought. Extreme droughts, such as the 8-year-long dry period from 2015-2022, can kill 40 to 80% of long-lived plants, and because perennials do not maintain seed banks there is only limited regeneration of these after drought-breaking rain. Annuals, such as Gazania lichtensteinii (Asteraceae), emerge in their masses, saturating the landscape with colour and scent. This is a cue for the emergence of solitary bees which can remain dormant for months or years.
The barren ground of a deflation hollow which is home to so much insect diversity (left) and the vegetation surrounding the deflation hollow (right).
Most solitary bees nest in the ground and eroded patches and paths are favoured. During my studies, a seemingly desolate stretch of land caught my attention. This area, characterised by hard sediment, served as a shortcut from the jeep tracks to a wild colony of honeybees nesting in an aardvark (antbear) burrow.
The flora surrounding this bare ground is a stark reminder of the Karoo’s remarkable resilience, showcasing a rich tapestry of species that thrive in one of the world’s most harsh climates. Yet, amid this tenacity, certain areas of the landscape remain barren and hardened—perhaps trampled centuries ago by fat-tailed sheep held in corals overnight to protect them from predators, or more recently, during the 19th century when the natural rangeland was stocked way over the capacity of the vegetation to recover.
Not long ago, I buried a wild hare—a tragic victim of roadkill—in an aardvark dugout: a deep, empty cavity in an area of hard ground I could never have dug myself. My sister, with her characteristic humour, had remarked, “Everyone needs an aardvark.” Indeed they do. For Aardvarks (Orycteropus afer) are extensive burrowers in sub-Saharan ecosystems, actively modifying their environment in the construction of shelters, and in excavating termitaria for food. This, in turn, generates nest sites and unique habitats that support a variety of other species. Burrows of aardvarks are used as shelter by foxes, porcupines, suricates, birds and honeybees. Moreover, when their large burrows collapse they form dams that capture seeds and water and initiate vegetation regeneration. As I reflected on the hare’s untimely death, I was once again captivated by the number of solitary bees nesting in holes on the inner edges of these burrows. Like the wild honeybees in these landscapes, many species are dependent on the aardvark for their nest sites; a reminder of nature’s interconnectedness. All around the dugout vibrant yellow swathes of Gazania lichtensteinii (Asteraceae) were in flower, their annual beauty enhanced by early winter rains.
The seemingly lifeless stretch of ground, a wind-scoured deflation hollow, was located close to this dugout. Deflation hollows form where vegetation is lost allowing wind to remove sandy topsoil and expose a hard subsoil comprising desert dust cemented with calcium carbonate. They are often associated with stone age human settlements of hunter-gatherers and herders. At this particular deflation hollow, there are various stone tools made from chert including a stone arrowhead. Standing on this hardened ground I was struck by a common misconception: that bare earth signifies death. Often ignored in environmental assessments, this apparently barren, hard ground was, in fact, teeming with life and intrigue. Initially mistaking the sounds I was hearing for a drone congregation area—where honeybee males dart through the sky waiting for a queen—I quickly realised that the sound was emanating from the ground.
Male Tetraloniella solitary bees congregating around the nest holes, waiting for the females to emerge.
A closer look revealed a fascinating gathering of male Tetraloniella bees. These short-horned, longhorn solitary bees were eagerly vying for a chance to mate with a female as she emerged from her underground nest.
Although solitary by nature—females work alone in building nests and provisioning food—these bees form dense aggregations in favourable environments. The apparent barrenness of the ground belied its role as a prime breeding ground, and I counted an astonishing 114 nests in the vicinity.
The evolutionary journey of bees, stretching back around 100 million years, began with solitary, predatory mud-dauber wasps, coinciding with the rise of flowering plants. Today, bees exhibit remarkable diversity. They range in size from a mere 2 mm to 39 mm and come in various forms, from densely hairy to smooth and shiny, often adorned with striking colours and patterns. Most species of solitary bees prefer to nest in the ground, often utilising plant materials or resin to line their nests. On this hard, bare ground, the thriving community of Tetraloniella served as a vivid testament to the vibrant life hidden beneath the surface.
The deflation hollow measured 24 m by 13 m, with nests concentrated in a mere 12 square metres. The solitary male bees have one primary role: to mate. To prepare for mating in the earlier hours of the day, the males press their bodies against the sun-warmed sand, basking to boost their speed for the frenzied mating rituals to come. Many were covered in bright yellow Gazania lichtensteinii (Asteraceae) pollen, evidence of their flower visits for a source of energy-rich nectar.
In addition to the Tetraloniella, there were other species thriving in this environment. Among them were various species of leafcutter, dauber and mason bees (Megachilidae) that make their nests in pre-existing burrows. The leafcutters were using both leaves of Lessertia annularis (Fabaceae) as well as petals of Gazania lichtensteinii (Asteraceae) to construct thimble-like cells. One of the females used chewed reddish-pink plant pulp to line her burrow walls. The collected pollens for provision of larvae with food were from plants different from those used for nesting materials, possibly from Melobium candicans (Fabaceae) or Rushia bijliae (Aizoaceae), both in flower and in range of the nest sites and on which Megachilidae were sighted.
Leafcutter, dauber and mason bees thriving on the deflation hollow.
Tetraloniella female foraging on Berkheya spinosa (Asteraceae) (left) and leafcutter bees on Rushia bijlae (Aizoaceae) (centre) and Melobium candicans (Fabaceae) (right).
A closer examination of the ground revealed a Camponotus rufopilosis ant carrying a dead conspecific. With mandibles featuring 5 to 7 teeth, these ants defend themselves by spraying formic acid when threatened. Meanwhile, a brown-and-white striped fly (probably in the genus Parisus) hovered above a bee nest, rapidly depositing 33 eggs. This Bombyliidae fly is known to parasitise a range of insects including bees. This observation might represent a new host record, and underscores the intricate relationships between host and parasite.
The climax of my observations came when a chaotic scrum formed around a single nest hole, where male bees gathered in a frenzied attempt to mate with the emerging virgin female. As mating commenced, the male, mounted on the female, used his antennae to possibly fan a courtship pheromone believed to induce receptiveness in the female. Clasped tightly to her, other males attempted to dislodge him, displaying a complex mating struggle.
While at the study site, I saw numerous other creatures including lizards (rock agama and Namaqua sand), cryptic Sphingonotis grasshoppers, beetles, robber flies (Asilidae), and a wingless female mutillid wasp, entering the nest of a solitary bee by using her abdomen to push aside stones. I also heard barking geckos and, with much patience, managed to photograph one in its burrow. Overhead many kinds of birds flew by, including two pale chanting goshawks. Beyond this deflation hollow, I discovered an extraordinary nest in the shallow of a stone with a Chalicodoma mason bee sealing it closed with mud.
Camponotus rufopilosis ant carrying a dead conspecific (top left) Parisus fly laying eggs (top right) Cryptic Sphingonotis grasshopper (centre left) Mutilid wasp (centre right) Barking gecko (bottom left) Pale chanting goshawk (bottom right).
This study illuminated a critical lesson: even the most unassuming, barren stretches of land may be far from lifeless. They may harbour intricate ecosystems teeming with life that defies initial perceptions. The conservation of these natural ground-nesting habitats is crucial. Therefore, these often-overlooked spaces must be included in environmental impact assessments, as they may support complex and often unnoticed biodiversity, and may be vital for the survival of solitary bees and other species. Though tiny, bees and other insects are the architects of entire ecosystems. Through pollination, they shape which plants thrive or fade, ultimately contributing to the plant composition of particular regions. This, in turn, largely determines the composition of insect communities that maintain overall biome structure.
Bare ground is too rich in life to be ignored; recognising such ecosystems is essential for maintaining biodiversity and ecological resilience, while still allowing for erosion control and restoration efforts such as reseeding rehabilitation and replanting on damaged lands to enhance ecosystem health. While much restoration effort in rangelands is concentrated on revegetating bare ground, some hard, bare soil patches should be left as habitat for specialised soil-nesting bees and pollen wasps. Diversity begets diversity.
For readers interested in a deeper exploration of wild honeybees and solitary bees, we invite you to refer to our published paper in The Science of Nature and to visit our website for additional resources and information.
