Burrowing mammals actively change their environment, and provide valuable microhabitats used by other species. These burrows offer other animals vital thermal refuges from temperature extremes and environmental fluctuations particularly in hot arid and semi-arid habitats.
The architects of the burrow
All structures have stories to tell. At Wolwekraal Nature Reserve in the arid succulent Karoo region of South Africa, three wild honeybee nests were located in aardvark burrows. 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, amongst them also cavity-dwelling honeybees and the numerous other creatures that co-exist in a wild nest. This article looks at the ecology of the honeybee nest site, and the dependence on the honeybee for numerous creatures as a source of food.
Honeybees are cavity dwellers
Nest 1, an aardvark burrow with a colony under a sandy rim
Honeybees are cavity dwellers. At Wolwekraal trees are scarce and rock cavities are a rare sight. Dwellings, much like the food supply, are transient. Wolwekraal is situated in the Karoo Basin which once formed a deep, inland sea. Through the erosion of the mountains to its south and of the landscape towards the north, a cycle of sedimentation began. Over hundreds of millions of years layers of sediment were deposited some 3km deep, and later tilted to form the seemingly endless horizons north of the village of Prince Albert. This area supports many different and unique plants, adapting to extreme climatic conditions together with their pollinators, including the honeybee. This is also where the aardvark roams.
It has been suggested that the limiting factor on the number of wild honeybee colonies in any area is determined by the worst month when there is little forage. In this desert region, not only is forage challenging and limited in the hot summer months with very little other than the Vachellia karroo in flower, but also the availability of nest sites. The three wild honeybee nests located at Wolwekraal all lie along a single north flowing minor drainage line west of the Dorps river in aardvark burrows situated on deep alluvial sediments. Aardvarks avoid areas of solid or rocky ground, preferring a sandy, loose soil optimal for digging. Aardvarks are skilled burrowers, and their tunnels provide crucial thermal refuges in the extreme temperatures of the Karoo, where summer highs often exceed 40°C and rainfall is scarce. These burrows help maintain a more stable climate, with internal temperatures ranging from 25°C to 32°C, offering a respite for many species. For honeybees, whose ideal brood temperature is around 35°C, these burrows provide an ideal nesting environment. 35°C is also an ideal temperature for the moulding of wax comb by honeybees.
Nest 3, a small colony situated between two aardvark diggings that are connected
The importance of shade
One of the key benefits of these aardvark burrows is the shade they provide. The relentless heat of the Karoo can make the ground scorching—often 10°C to 20°C hotter than the air. Even the sparse shade from the branches of the Vachellia karroo trees offer some relief from the heat. It is therefore not surprising to see a vast diversity of other creatures sharing the dwellings which honeybees inhabit.
Co-habitants of the nest
Termites were the first co-habitants noted in the documented nest sites. Aardvarks, in excavating these cavities, were, of course burrowing for termites upon which they feed. Over the current study period of 12 weeks, only twice did it appear as though one of the three honeybee colonies had been attacked by termites. The skirmish with the guard bees was short-lived and within a day dead termites and honeybees were removed from the nest by worker bees and dropped at distances of 20m – 50m from the colony. In environments where food is limited, it does not take long for the dead to be predated on. Immediately Pheidole and other ants arrive on the scene to carry off the bodies, as do beetles such as the Eurychora sp., commonly known as mouldy beetles. Several mouldy beetles have been documented living side-by-side with honeybees in two of the three aardvark burrows. If bees detect incursions by chemical means, it would appear as if these beetles, by covering themselves with soil and nest debris and by rubbing soil particles on each other—as documented at one of the nests—would possibly use this form of camouflage to be able to move around the periphery of the nest largely unhindered by the honeybees. Soil and vegetative debris is adhered by bristles and waxy filaments on these beetles’ backs. Mouldy beetles are detritivores, feeding on dead plant and animal litter. Such detritus is an important component of food reserves in desert regions. As such, honeybee nests offer a constant concentration of detritus to support this population. Other beetles documented in these nests include the tortoise darkling beetle (Epiphysa flavicollis) which scavenge plant and animal material at night and live for many years.
The role of wax moths and other detritivores
Other detritus feeders are the larvae of the greater and lesser wax moth, Galleria mellonella and Achroia grisella respectively. These larvae are mostly tolerated by wild honeybees as they play an important role in maintaining nest hygiene. They help by cleaning out sections of old wax comb and are frequently found feeding on leaf litter, beeswax particles, and pollen present in the nest debris.
On the Cape Peninsula an abandoned honeybee nest in a cavity situated under rock was documented. In the nest were numerous wax moths and the deserted wax comb was writhing with wax moth larvae. In addition, two shrews made their home in the nest, benefiting from the plentiful food source provided by both the larvae and the moths. Once the larvae have cleaned the comb and both they and the shrews have departed, the nest becomes ready for re-occupation, illustrating the ingenious cycle of nature. The role of the wax moth is thought to be that of a scavenger, helping therefore to control potential diseases much like hyenas do in their ecosystems. Interestingly, the moths and the larvae continue to play a role even while the bees occupy the nest.
Shrews on the Cape Peninsula feeding on wax moth larvae
A diverse community
Skinks, too, are found feeding on wax moth in honeybee nests. In addition, the variegated skink (Trachylepis variegata) was seen feeding on small invertebrates like ants and flies. Flies abound at every honeybee nest site. Rondanioestrus apivorous, a bee tachinid, lays eggs on bees in the air as they fly into their nest. The egg almost immediately hatches into a larva which feeds on the soft tissue of the honeybee until it is ready to pupate. The bee conopid, Physocephala fascipennis with its distinctive hourglass abdomen does the same. In addition, the Blue-green bottle fly of the Lucilla sp. is also a regular visitor to the nest as are the robber flies of the family Asilidae.
When a small number of Banded bee pirate wasps (Palarus latifrons) were documented at two of the three nest sites, the wasp, upon catching a returning forager flying into the entrance of the burrow, would fly off in the direction of its nest followed by a scurry of small jackal flies. These kleptoparasitic milichiid flies (Desmometopa spp.) feed on :haemolymph rich in nutrients, and they typically steal food from other insects. They are thought to be attracted by a chemical pheromone given off by the injured or stressed honeybee, and they need to be fast to keep up with the flight of the much larger predatory wasp. Banded bee pirates are most active when temperatures are between 24C and 40C. Their diet consists largely of honeybees. The wasps compete with each other for prey, each vying to catch a honeybee, darting back and forth across the nest entrance and diving at each other. The captured honeybee is stung and paralysed by the female wasp and taken to its burrow where she lays an egg on the bee. The egg hatches into a larva and consumes the bee. Other wasps, such as the Bembix wasp, have also been noted flying higher above the nest site. Bembix hunt their prey on the wing, often catching forager bees flying off or returning to the nest. Bembix typically prey on flies of various families, however not exclusively, as seen at the wild honeybee nests and where honeybees are foraging on the sweet thorn (V. karroo).
Top row: Banded bee pirate wasp carrying off a honeybee caught on the fly. Bottom row: numerous fly species wait at the nest entrance to lay eggs on returning foragers
Ants are so important in the ecology of a wild honeybee nest and are ever present in the nest. They are constantly contributing to nest hygiene by carrying away dead bees and other organic matter including seeds blown into the burrows. Seeds are also carried out by the bees themselves, thus both ants and honeybees are vital to seed dispersal, with ants playing a much larger role. While ants are tiny, they have a really large ecological impact. In the wild certain species may be tolerated by honeybees and we have documented ant nests side by side with wild honeybee nests, separated by a good portion of propolis. As long as there is a healthy balance, ants and bees, which are related, both being of the order Hymenoptera, coexist in close proximity, as do the termites and the honeybees at the nest site at Wolwekraal.
A balbyter ant (Camponotus rufopilosis) carrying a dead honeybee into its nest
Spiders, too, find their place within these burrows. Some spiders tunnel into the walls, and Pholcid spiders (daddy-longlegs, cellar spiders) hang upside-down in their haphazard webs. They rely more on the irregular structure of the web to trap honeybees returning to the nest, rather than it having adhesive properties. Upon detecting struggling prey these spiders swiftly wrap their prey with silk-like material, either eating it immediately or storing it for later. Jumping spiders (Salticidae) do not spin webs, but are free-running and actively stalk any prey they detect, and are often found on the soil surface. They are known to have the sharpest vision of all spiders, along with tactile chemoreceptors on their pedipalps. They mostly specialise in preying on ants which are usually plentiful, but generally prey on a wide range of insects and other spiders, and prey may sometimes include a honeybee.
Observing nature’s complexity
The diversity in these extreme environments is surprising. So often one is reminded of the extraordinary privilege of being able to still wander in such untouched spaces; or in areas that were once farmed but have been allowed to bounce back again boasting bygone beauty. This phenomenon is particularly evident in the case of wild honeybee colonies established within burrows, where the bees thrive abundantly and do not perceive humans as threats to their resources or existence. Instead, observers are presented with the unique opportunity to engage in passive observation, immersing themselves in an alternative ecosystem characterised by intricate ecological interconnections that often transcend human comprehension. It is as if one enters a state of mindfulness previously unexplored.
SELECTED REFERENCES
Begg, J. (2005). A Ramble through the Rocks of the Swartberg, Prince Albert (Kweekvallei), 88-96.
Dippenaar-Schoeman A.S., Van den Berg M.A. & Van den Berg A.M. (2001). Salticid spiders in macadamia orchards in the Mpumalanga Lowveld of South Africa (Arachnida: Araneae). African Plant Protection 7(1): 47–51.
Gess, S.K.& Gess, F.W. (2014). Wasps and bees in southern Africa. SANBI Biodiversity Series 24.
Haddad, C.R. & Dippenaar-Schoeman A.S. (2002). The influence of mound structure on the diversity of spiders (Araneae) inhabiting the abandoned mounds of the snouted harvest termite Trinervitermes trinervoides (Sjöstedt). Journal of Arachnology, August 2002.
Heiduk, A., Brake, I., Shuttleworth, A. and Johnson, S.D. (2023) “‘Bleeding’ flowers of Ceropegia gerrardii (Apocynaceae-Asclepiadoideae) mimic wounded insects to attract kleptoparasitic fly pollinators,” New Phytologist.
Henschel, J. R. (2021).Long-Term Population Dynamics of Namib Desert Tenebrionid Beetles Reveal Complex Relationships to Pulse-Reserve Conditions. Insects 2021 Sep; 12(9): 804.
Hepburn, H.R. (1986). Honeybees and Wax, An Experimental Natural History. Springer Verlag, 205 pgs.
Knöthig, J. (2005). Biology of the Aardvark (Orycteropus afer). Diplomarbeit, Fakultät für Biowissenschaften der Ruprecht-Karls-Universität Heidelberg.
Milton, S. J., Short, S., & Dean, W. R. J., 2022. Decline in whistling rat (Parotomys brantsii) density: Possible response to climate change in the Karoo, South Africa. African Journal of Ecology, 60, 969–979.
Pike DA, Mitchell JC, 2013. Burrow-dwelling ecosystem engineers provide thermal refugia throughout the landscape. Animal Conservation, 16, 694–703.
Tribe, G. (2009). Creatures inside the hive, Village Life No 34, Autumn 2009.
Tribe, G. (2021). Honey Mountain. Pinewood Studios, Cape Town. 216 pgs.
Weyer, N. M. (2018). Physiological flexibility of free-living Aardvarks (Orycteropus afer) in response to environmental fluctuations. Faculty of Health Sciences, University of the Witwatersrand, Johannesburg.