In Southern Africa, fungus-growing termites, which build enclosed mounds without visible ventilation holes belong to the genera macrotermes. These macrotermes mounds can be up to 6 meters high above ground. The tip nearly always leans slightly over and the termite mounds face North, which can be taken as a reliable direction pointer.
Generally spoken, such mounds consist of the outwash pediment, a conical base, and the spire with the tip on top.
Outwash pediment of termite mounds
The base area of and around the mount is called the outwash pediment. It is free of vegetation and just consists of hard-baked termite mound material. This material was eroded by rain, wind, and sun from the base cone and spine. It is a mix of quartz grains, which are glued together by clay particles and termite saliva. Research has shown that each year about 1 cubic meter of mound material will be washed down. And the same volume will be built up by the termites again.
The size of this base area depends on a variety of factors. But for us, it is important, that it is also a reliable indicator of the direction East. Early morning, carnivores are often laying up in the east of the mount. They want to receive as much early sun as possible after a cooler night. And as the outwash pediment is free of vegetation and dry – which many of the carnivores prefer. The favorite laying-up areas of leopards, cheetahs, lions, but also mongooses, at such mounds are often very visible. It will be free of loose material and sometimes even appear shiny from long-time regular use. And it is always located in the east of the mound.
The conical base of termite mounds
The conical base is the lower uprising part of the termite mound structure. Outside it is a hard-baked shell and inside a porous structure with a multitude of chambers and channels. The conical base is in many cases too step for laying up of mammals. In an active mound, the conical base is just used as an elevated observation tower for men and beasts. But when the termite colony dies out, the former active mound will be colonized by a variety of insects, arachnids, and reptiles. Humans have a special use of these conical bases of some inactive Macrotermes mounds. They dig a hole into it and use this cavity as a baking oven.
The spire of termite mounds
The spire ends at the tip, which is our direction pointer. In the southern hemisphere, the sun rises in the east, moves over the north, and settles in the west. The sun’s position is highest in the north. And therefore the termite mounds face in this direction.
There are at least four theories, to why the termite mound tip is slightly leaning over to the north. These theories are:
Prevailing wind direction
The latest research by Fagundes TM, Ordonez JC, Yaghoobian N. 2020 has shown here that wind does not influence overall over-ground mound shape but only internal mound structures and temperatures.
Magnet field influences
The influence of magnet fields is only confirmed for Amitermes meridionalis, commonly called compass termites. Their distribution is confined to the Northern Territory of Australia, specifically around Darwin. For Southern Africa, such magnet field influence could not be proven.
Partial drying out of the spine
This theory assumes that the heat from the sun is highest in the NNW-NW direction. Therefore the chimneys within the spine dry out more on this northern side. And therefore the tip is leaning over in this direction. Noon is not the hottest time of the day, as the heat of incoming sunrays is still increasing. Only after around 3 pm, does the outgoing heat from the earth start to get higher than the incoming heat. An effect due to a lower sun position. The most heated part of the termite spine is therefore facing the North-North-West (NNW) to the North-West (NW) direction.
Average zenith angle
Measurements have shown that the tip of the termite mound always points to the average zenith angle of the sun. If a location in the southern hemisphere is at 20 deg latitude, the tilt of the tip will also be 20 deg to the north. And at the equator in Kenya, the sun will stand directly overhead. And there is no tilt of termite mound tips.
At a healthy termite mound, the erosion rate and new build-up rate are in equilibrium. On the side illuminated by the sun, the metabolic rates of termites will be faster compared to the cooler side. And with a higher metabolic rate, also the working speed of termites increases. Therefore, the mound will grow with an increasing tilt. At least until temperatures and related soil transport rates are uniform over the whole surface. The weak point of this theory is that during the summer solstice north of the Tropic of Capricorn, the sun moves a few degrees into the southern sky. Will termites also build the tip of the spine towards the south during this occasion?
Summary of these theories
Both theories, ‘Partial drying out of the spine’ and ‘Average zenith angle’, have got their followers. And it is not finally established which is the correct one or how both theories interact. Scientists will find the correct answer in time. What we know is the effect that in Southern Africa, tips of Macrotermes termite mounds will in the majority point towards the North.
Lessons learned from finding direction North by Macrotermes termite mounds
- Macrotermes termite mounds have a conical shape and generally only one tip
- This tip leans toward the direction North
- Currently, two theories try to explain the reason why this leaning toward the North happens
