Geoff Tribe & A. David Marais
Four nesting sites have thus far been located on a 900ha farm in the Succulent Karoo north-east of Touwsrivier (33° 21’S 20° 03E). Two of the nests were found under shallow overhangs on rocky ridges, one that occurred alongside a dry river course and the other in the foothills of the surrounding mountains. The other two nests were located deep in deserted aardvark burrows, one just above a dry water course and the other on a plateau.
Where honeybees nest is largely determined by the environment in which they live.
While winter temperatures may plummet as low as minus 4°C, summer temperatures of 41°C have been recorded on the farm “Zoethoek”. Crumbling shale forms the dominant rock formations which is not conducive to the formation of cavities or small caves, and hence the relative dearth of rock-rabbits (dassies) on the farm who prefer to live among boulders. The average rainfall for Touwsrivier is 240mm, of which most falls during the winter months, but rainfall may be fairly erratic. The dominant trees, almost all of which occur along the dry water courses, are Vachellia (Acacia) karroo, Searsia (Rhus) lancea and Searsia undulata, none of which could provide nesting sites due to their small stature. Vachellia karroo is only one of two plants flowering on Zoethoek in January and hence attracts a myriad insect species from bees, wasps, flies and beetles of many species, including the fruit chafer Rhabdotis semipunctata (F.).
The only permanent water is to be found in a reservoir served by a windmill on the eastern border of a neighbouring farm at which honeybees are invariably seen collecting water. The highest mountain rising above the plains at 800m above sea level is the Rooiberg at 1052m.
Shepherds in the past had constructed a rudimentary cairn of rocks about the nest under the overhang alongside the river course presumably for some protection of the nest against the elements, and one reason for this could be to ward off the intense summer heat. When the second nest was discovered (also with a partial cairn of rocks around it), the wax and propolis had melted presumably due to the intense heat and the bees were present in very low numbers at the very rear of the cavity. Possibly it was not only the atmospheric temperature which was to blame, but also the heat accumulated in the rocks themselves, because any rock that is picked up is extremely hot. During the hot summer months water becomes essential to cool down the nest – forcing honeybees to collect water from a leaking pipe when the temperature was 36°C.
It appears that nesting in aardvark burrows is perhaps the best recourse for the honeybees. There is always the potential danger of the burrow being flooded but rainfall in this region is meagre. Nests deep in such burrows are less affected by extremes of temperature and the bees are better able to control the humidity within the nest. The nest on the plateau has been there for at least a year and appears to be thriving.
The photo of bees clustering about their combs was taken at 06h00 at a temperature of 14°C.
The water course colony had used the outer combs to form a ‘wall’ which they had propolized together, restricting the entrance and so effecting better control over both temperature and humidity.
When this nest was discovered, a loud ‘moaning’ sound emanated from the burrow – a sound which is heard when honeybees are plagued by the banded bee pirate wasp, Palarus latifrons (see photos below).
All the nests on the farm had banded bee pirates in attendance outside their nests which catch incoming or exiting bees and bury three paralysed bees in a specially constructed burrow and onto which they lay a single egg. The hatching larva then feeds on the bees. Up to 80 banded bee pirates have been counted around a bee hive in the Swartland, with a female wasp capturing a bee every 10 minutes or so and provisioning many burrows. The bees become so intimidated that they refuse to leave the hive and set off a ‘moaning’ sound, the reason and effect of which is as yet unknown. Does it warn the foraging bees of the imminent danger or threaten the wasps to keep their distance? How is this knowledge of danger transmitted from the foragers to the rest of the hive as this ‘moaning’ sound is restricted only to the presence of the banded bee pirate? How is this sound produced – and from which part of the bees’ body? To have this sound produced by the entire colony indicates the extreme danger that these wasps present to the honeybees. Often, as the sun sinks and the banded bee pirates depart for the night, the honeybees make a desperate effort to collect nectar and pollen before night falls. Sometimes the colony begins to starve and is forced to abscond.
Tape recording the ‘moaning’ sound and playing it back to honeybees in an observation hive to elicit a response could possibly help determine the effect of this sound on the colony. The frequency of the sound may be just as important because many sounds produced within the hive are carried through the substrate. For example, the movement of a ‘piping’ queen in an observation hive can be followed on the other side of the comb by the path of ‘frozen’ workers. One effect of ‘piping’ is to ‘freeze’ the workers around the queen, a mechanism used also by the death’s head moth (Acherontia atropos) when entering a hive, but in this case the sound is not produced by the wings but through the moth’s proboscis.
Many more honeybee nests have yet to be discovered on the farm as bees collecting water leaking from a damaged pipe indicate the presence of other colonies in unexplored parts of the farm. Most of the bees are dark and appear to be Apis mellifera capensis, and the farm does fall within the winter rainfall region, albeit on the northern margin of its distribution. A determination of the number of ovarioles of a sample of worker bees would confirm whether they are Cape Bees or Apis mellifera scutellata.
Because no honey badgers (ratels) have as yet been observed on the farm, only baboons, banded bee pirates, and robber flies (Asilidae) appear to be the only creatures that threaten the existence of the bees.
ABOUT THE AUTHORS:
Dr Geoff Tribe is a Specialist Researcher – Entomology, Plant Protection Research Institute (retired), has done research on dung beetles, honeybees, forest entomology, slugs & isopods and is our project mentor.
Dr A David Marais is a Professor in Chemical Pathology at the University of Cape Town Health Science Faculty. Both Dave and Geoff have a mutual interest in the Stapeliads – the carrion flowers which emit a stench and are pollinated by a variety of flies and not by bees!