As part of World Soil Day, we want to tell the story of what lives below our feet; insects, earthworms and the soil cycle gardeners rely on so heavily to create luxurious earth. Candide entomologist, Nina, tells the beautiful tale of the food web annual cycle.
The soil year
The story begins above ground. It’s August, and the leaves are still green. Soon the new generation of queen bees will emerge to mate, before finding the perfect spot to hibernate until the following spring. Plants are working hard to squeeze in one last burst of growth, absorbing the remaining sunlight as the evenings begin to arrive sooner and sooner.
By September, the mornings begin to darken, and the leaves start to fade into an array of reds, oranges, yellows and browns.
Leaf-litter is now beginning to form. So what happens to all the fallen leaves? And what happens to the old trees that fall, or the food we throw in the compost heap?
You might recognise the term food web. A food web is a community of animals and microorganisms going about their day to day lives. It highlights the interactions that are taking place in a specific ecosystem, involving a transfer of energy. Ultimately, these interactions cascade in all kinds of directions, until reaching the very top predators, which in most cases, are us, humans.
A basic soil food web diagram
One of the most essential food webs is under our feet, in the soil. The soil is an extremely productive place, teeming with life. To start, let's hover at the surface.
Leaf litter and plant debris provide the perfect wildlife corridors for our garden minibeasts.
A corner of the garden that’s left to grow provides a refuge for hedgehogs, toads and beetles. Here, you might find a violet ground beetle looking for dinner, and if you look closely enough, you may see a female wolf-spider with her egg-sac delicately attached to her abdomen. She’ll carry her babies on her back until they’re mature enough to fend for themselves. With them, she sits and waits, perfectly camouflaged, ready to ambush the next fly, caterpillar or slug that passes!
At night, predatory centipedes are also active. They patrol the topsoil in search of woodlice, harvestmen, spiders, springtails and beetles!
The brown centipede is one of several centipede species found in the UK
Now let’s delve further into the soil. Beneath the surface, you can find hundreds of thousands of bacteria, protists and fungi. They are so small we humans can’t see them, but they help to regulate soil moisture, airflow and temperature. Other, slightly larger creatures then eat these microscopic organisms.
Mites are poorly studied and are so small that they often go unnoticed. But these creatures make up one of the largest groups of soil organisms, displaying a wide variety of specialist diets. We know them well as pests, but some scientists believe that a diverse population of mites dramatically increases the rate of soil formation.
There are over 600 species of soil mites in the UK. Credit: from British Oribatiae via Biodiversity Heritage Library
Moving on, we have the woodlice, bristletails, millipedes and symphylans; often referred to as the soil shredders. These creatures spend some time under the soil, but can also be found above ground, under rocks or on decaying wood. Here, they graze on bacteria, fungi, organic matter and plant debris. In doing so, they convert large, less valuable pieces of organic matter into a nutrient-rich mush, known as humus (not the kind you dip your carrots in!). Occasionally, these shredders will attack plant roots, but ultimately the overall good they do outweighs the bad.
Finally, we have the annelid worms. There are approximately 7,000 species of earthworm; they’re probably one of the most important animals in the world. We call them ecosystem engineers because they alter the structure and conditions of the soil disproportionately to their size.
Earthworms feed on organic soil matter. They produce byproducts known as casts, which they leave in their tunnels and burrows. They provide a niche that’s rich in nutrients, with space that’s ideal for plant roots to grow in.
There are over 7,000 species of earthworm
Not only does the burrowing behaviour contribute to soil mixing, but at the same time, it creates small chambers of air. This accelerates the chemical reactions going on within the soil, removing any undesirable CO2. Check out this article on soil structure to learn more.
Shrinking ourselves down again, you’d come across nematode. You may know nematodes as parasites, or, you may know them from the treatment you apply to your lawn. These kinds of nematodes naturally occur in the soil. They’re good friends with particular types of bacteria, which they work together with to find prey. A nematode will incorporate bacteria into its intestine before entering the cavity of the victim (yikes!). While the bacteria multiples, the nematode is also completing its life cycle, giving rise to more nematodes. Their primary victims are beetle and fly larvae, making them an excellent addition to your soil media.
Nematodes are a handy ally to get rid of pests
There are thousands of different interactions that go on in the ecosystem, and most of them we can’t see. Nonetheless, the outcomes of these interactions can benefit soil structure, nutrient content, soil drainage, as well as removing harmful pests, bacteria and chemicals from the soil.
Keeping your soil happy comes hand in hand with keeping those who inhabit it satisfied. The first step is to know your soil and do your research. Pesticides and fertilisers can be appropriate in some instances but are not always necessary. They can dramatically alter the soil composition and interactions that go on. Look into any products thoroughly. They can contain strong chemicals that may persist in the soil for years afterwards.
To find out more about your garden's soil type, read our article on Working With Different Soil Types!