This mild winter is a good time for looking at the activity of earthworms. The soil is moist and our lawns are a mass of worm casts, a mix of worm excrement and soil. The number of small coiled piles of worm casts tell us that there is indeed a great deal going on under the surface and it’s interesting to think about just what is happening under there. What are they doing?
They’re doing what every being does – gathering food, eating, resting, reproducing – just in their own wormy way. I see a lot of worms in the course of my work and have long got over the ‘Ewww!’ reaction, to see them as both fascinating and vital to soil and plant health. As they move through the soil, worms turn and aerate it, improving structure and drainage. They also increase a soil’s nutrient level by pulling plant matter under the surface; once digested and excreted, plant nutrients such as nitrogen, phosphates and potash become more accessible to surrounding plants.
Some years ago, I visited Charles Dowding’s vegetable garden in Somerset to see his ‘no-dig’ set up. He doesn’t dig the soil there, preferring to mulch with compost so that the soil structure remains undisturbed. One of things he said that stayed with me was that, on average, an inch of compost spread over the surface of a plant bed would have pretty much disappeared within three months, having mostly been pulled down into the soil by the worms. After that, I examined a vegetable bed in my own garden, one that was mulched with old hay, to see what was going on underneath. When I carefully lifted some of the hay, I could see that parts had been gathered and twisted into rope-like lengths which were slowly disappearing into what could only be worm holes.
You don’t have to spread compost or hay to see where plant matter is being used by worms. Go out onto a piece of ground that has fallen leaves or plant debris and look closely at the soil where worm casts are plentiful. Some of the leaves will be upright, furled and apparently embedded in the soil. These are on their way to a worm’s underground food store, called a ‘worm midden’, where they will decay for a while before the worm eats them. Worms will also protect the entrances to their middens by placing small stones around them, which is shown in this video clip.
So, how many worms are there? Looking into it, I found that the Rothamsted Experimental Institute estimates that ‘rich fertile farmland may have up to 1,750,000/acre (432/m²), meaning that the weight of earthworms beneath the farmer's soil could be greater than that of his livestock upon its surface’. Now think about how many worms there might be at, for example, RHS Wisley, where there are some 240 acres of fertile and well-planted ground. If each acre is inhabited by 1,750,000 worms, that means there could be as many as 420,000,000 worms there. Imagine that.
I suppose that the moral of this story is, look after your worms and they will look after you.
Video of worm eating a leaf stem