Ever thought about Earthworms?

23 Oct 2022

Written by Dr Julia Baum

Earthworms, similar to bees or ants, play key engineering roles in natural systems and thus directly affect our lives. Let’s dig a bit deeper to understand why.

Did you know that there are about 7,000 different species of earthworm living beneath our feet? Only around 150 of these earthworm species, however, are widely distributed around the world. 

It is said that the mass of all earthworms living on our planet is greater than the mass of any other terrestrial animal species. They can vary in size from about 10 mm to 3 meter. 

The giant African earthworm (Microchaetus rappi), for example, reaches average lengths of 1.4 meter (4.5 feet).

Earthworms belong to the phylum Annelida and are cylindrical, segmented worms. They are found in varying depths of the soil body, generally feeding on living and dead organic material. They are further classified into three groups according to their behaviour and habitat, namely epigeic, endogeic and anecic.

Epigeic earthworms live on or very close to the soil surface where they feed on rotting plant and animal material and do not dig tunnels.

Endogeic earthworms live in the top 10 cm to 30 cm of the soil body where they form horizontal tunnels. They ingest soil particles in order to absorb nutrients from degraded organic material.

Anecic earthworms dig deep within the soil during the day where they form permanent, vertical tunnels but surface during the night to feed and deposit their casts. 

Soil health

Earthworm presence, or absence, in soils influences several soil properties which determine the overall status of soil health. From a positive perspective, their burrowing activity improves granularity and soil structure, for example.

Further, earthworms recycle dead organic material to compost by pulling organic material deeper into the soil through their tunnels or by ingesting and digesting it to form humus.

Overall, earthworms cause diverse physical, chemical and biological changes to the soil profile. These conditions affect nutrient availability for plants, habitat availability and activities of other organisms present in the soil system, aeration, water infiltration and drainage ability of the soil body, and more.

Of key interest, facing our current global challenges around climate change, should also be the capacity of healthy soils to sequester and store gigatonnes of carbon long-term. It is known that during the process of breaking down organic matter earthworms do release carbon dioxide, partially causing emissions from soils, however, their digestion process also produces a solid form of carbon which remains in the soil being locked up.

From a negative perspective, when earthworms are not abundant enough in the soil profile, conditions usually decline drastically and can lead to issues such as erosion, reduced water infiltration, compactness hindering the growth of plant roots, and more. 

Both physical (temperature, moisture, aeration and texture) and chemical properties (pH) of the soil determine the presence of earthworms. They are less active or abundant with decreasing soil moisture and increasing soil disturbance. For example, fertilizers containing nitrogen or other agricultural products with DDT, lime sulphur or lead arsenate can create acidity or poisonous conditions which are fatal to earthworms.

Generally, the more disturbed a soil body, the fewer earthworms can survive which leads to unfavorable outcomes. 

Healthy solutions

How can we consider earthworms in our future?

We have just understood that they play an important part in the cycle of soil health which in turn is directly linked to the provision of diverse ecosystem services. As humans, we strongly depend on healthy soils and ecosystems for our food production and other natural resource value chains. Ecotourism, wildlife ranching, wild harvesting of resources and any related activities face the same need for healthy soils. Soil is the basis for both functional agricultural as well as recreational and wildlife conservation systems.

Because farming touches around 50% of our global land surfaces, urgent emphasis has to be put on saving and again increasing the extent of healthy soil bodies. This is where conservation and any other environmentally-friendly procedures have to be integrated.  

A study in Vietnam, for example, found that agroforestry systems that are kept little disturbed and similar to indigenous habitats boost favorable conditions for earthworms because they provide greater vegetation cover and soil protection compared to more intensive farming practices and thus increase overall soil health (2021, World Agroforestry) 

At the African Wildlife Economy Institute we foster a discourse around increased sustainable use of wild resources such as plants, fruit, fish or antelopes going hand-in-hand with conservation of biodiversity and habitats while supporting businesses and livelihoods.     

The topic of soil health and earthworm protection, thus mainstreaming sustainable practices, is one of many complex examples where we can make a difference and focus on achieving real impact across landscapes. 

To learn more about regenerative agriculture watch our recent webinar ‘Harnessing the power of nature’ which we hosted in collaboration with ShareScreen Africa.

Dr Julia Baum, AWEI Partnerships and Conservation Entrepreneurship Advisor