Termite poo as seen from the air
You decide you need a holiday, so you book a flight over to Cape Town, at the southern tip of South Africa. As the plane descends, you look out of the window. The landscape starts to materialise, and you begin to notice these weird, regularly-shaped, almost circular shapes in the bush below.
They are heuweltjies (here-vil-keys). It’s an Afrikaans word meaning “little hills”, and these little hills are the fault of termites.
Heuweltjies aren’t the regular, hard-shelled termite mounds that tower like cathedral spires above the ground. They do still contain a central termite hive, but this is quite small, only a few meters wide, and mostly subterranean. The heuweltjies themselves are much bigger than just the hive, about 30 m in diameter and 1.5 m high, and roughly circular. They are so regularly organised (something that is a little unusual in nature) because of aggression between different termite colonies, each competing to set up a space to forage.
A typical termite mound (image by Justin Hall via Flikr) and heuweltjies in a wheat field (supplied by Mike Picker).
The termites that make these nests gather grass and leaves from the surrounding bush and bring them back to their nests. Here, they are eaten by the thousands of individuals that make up the colony, who all need to defecate. This poo (or frass, if it’s from an insect) is like small grains of sand, and needs to be disposed of. The unluckier members of the colony haul it up to the surface of the nest, where it sits in huge heaps. Nearly a ton of frass has been weighed on a single heuweltjie – that must have been dirty work, for both the termites and the researchers.
Termites often use their poo to construct parts of their nests. A mix of faecal matter, sand and other organic matter is cemented together with saliva (kind of like papier-mâché) to make intricate nest chambers. Image by Paul Asman and Jill Lenoble via Flikr
The termite gardener
The foraging of the termites concentrates the nutrients from plants in the surrounding bush to a small area around the nest. They are like tiny gardeners that make their own fertiliser and distribute it in the garden around their home. This has the same effect as fertiliser because the termite poo is highly nutrient enriched. It contains 15 times more calcium, 9 times more nitrogen and 17 times more carbon than the soils that surround the heuweltjies, and, as a result, the soil of heuweltjies is similarly enriched.
The enrichment means that different plants grow more densely on the heuweltjies than in the surrounding bush. They are often larger, bushier shrubs and the nutrient content of these plants is higher because of the richer soils. These larger plants trap and hold a lot of the sand that is blown around the landscape, which causes the hill to grow around the termite colony and produces the mound that becomes the heuweltjie.
So, heuweltjies are visible from the air predominantly because of the knock-on effects termite poo.
Insects love termite poo
It’s not only the plants that are influenced by the termite poo. Sheep prefer to graze on heuweltjies, and some beetles and flies even lay their eggs in the mounds of frass. Different invertebrates are found on the heuweltjies than in the surrounding bush, with certain species of beetle preferring to eat the heuweltjie plants, and some spiders preferring to eat these beetles.
Not only do termites influence the shape of the landscape around them, but they have knock on effects for plants, herbivores and predators. Sometimes, it’s the little things that have the biggest impact.