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.

Arial view of undisturbed heuweltjies on the right, and still visible once they have been ploughed over and planted with crops. Image extracted from Google Earth.  

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.

Daisies growing on heuweltjies in spring. Image supplied by Mike Picker. 

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

One of the spiders found more commonly on heuweltjies than in the surrounding bush. Photo through a dissecting microscope. Image author’s own. 

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.

Termite frass and the larger frass of beetle larvae (inset) that live in (and eat) the termite frass. Images author’s own.  

This post is based on a forthcoming article “Nutrient release by the termite Microhodotermes viator (Latreille) enriches its earth mounds (‘heuweltjies’) in the succulent Karoo (South Africa), and influences invertebrate communities” by G. L. Cornell, J Swanepoel, J. F. Colville and M. D. Picker.

4 Responses to “Termite poo as seen from the air”

  1. Kai Yee, Chan says:

    Interesting, great aerial image and photos accompanying your article.

  2. Jennifer Feinstein says:

    Really interesting article, Gabriel. Wondering if you have ever heard of biomimicry? Some buildings are built based on the structures of termite mounds in terms of the way they let light in etc.

  3. Gabriel Cornell says:

    Thanks Rob!

    You’d think so, but there hasn’t been much work done on that yet. I think there is some anecdotal evidence that porcupines or some other large rodent spend a significant amount of time burrowing for food on heuweltjies.

    I know that elsewhere in Africa, megaherbivores (including elephants!) have been shown to browse preferentially graze in the nutrient “sphere of influence” of more traditionally shaped termite mounds.

  4. Rob Dabal says:

    Interesting article Gabriel. They really are brilliant ecological engineers. Do other species use the mounds in some way, such as nesting sites? A few lizard species for example burrow into termite mounds to lay eggs as do Golden Shouldered Parrots in Cape York.