Is the common mole a soil canary?

Most gardeners and most farmers don’t like mole hills, but how many recognise the value of the mole? The last month or more has been mild in northern Scotland and it’s been boom time for busy moles in my part of the world. But it’s where the moles are burrowing that I find so interesting, or disturbing.

Why do I see more mole hills in the narrow verges of the main road to Aberdeen when I drive from my home to Elgin, than I do in most of the rich farm fields of the Moray Plain? Nowadays, most of these deep soils are used intensively for growing cereals with some break crops, but the days of mixed agriculture, using cattle dung in rotations, are mostly gone. The spring barley is being planted and the fields will soon flush that beautiful fresh green. Nowadays, though there’s rarely a mole hill to be seen. How different things are just inland, where I live, among the upland stock-rearing farms.

Across the road from our cottage stands one of my neighbour’s dung heaps and last month he was out spreading manure over his grass fields, later to be cut for silage. Moles are more obvious in these fields, which are regularly foraged for invertebrates by starlings and winter thrushes. Further up in the glens, I noticed on a recent visit that the permanent pastures were chequered with mole hills and I know that moles range high in the hills in the pockets of good soils.

So where have the moles gone on the low ground? It’s not that long ago that mole catchers were in great demand and, despite their best efforts with traps and poisons, the moles were never defeated. Is it deep ploughing that kills off moles? Or is it the intensive and continual use of artificial fertilisers and crop chemicals, in the absence of cattle dung rotations, which has killed off the soil invertebrates? Maybe both. The absence of moles in intensively-farmed fields may be a result of an absence of worms, their essential food.

I remember how annoying mole hills were when I used to cut hay for my cattle and sheep, using an old bar mower, and I’d hear the clatter of a mole-turned stone denting the blade. Despite that, I always remembered that worms and moles were an essential part of “keeping the land in good heart”. Charles Darwin called earthworms ‘nature’s ploughs’. The activities of worms enhance the fertility and health of soils; they work away at moving and decomposing plant material, aerating and stabilising soils, releasing nutrients, promoting plant growth and sequestering carbon. Goodness they pay their way. And the moles also create tunnels which help aerate the soils and allow water penetration, as well as being voracious feeders on invertebrates harmful to plants.

Information on moles in the UK is surprisingly scant. What is the scale of the decline of moles, and worms, due to intensive agriculture in say the last fifty years? I can find figures of a million worms per hectare in naturally fertile soils but what are the densities nowadays in fields of intensive cereals? I believe the loss must be truly massive. I remember the fields once hosting birds searching for invertebrates, blizzards of black-headed gulls following the plough and buzzards shuffling over winter cereal fields eating worms, where now I see none or very few.  I would like to know the scale of this decline and its effects on long term soil health. Might it be as alarming for humans in the long-term, as it is now to earthworms and moles? It’s probable that the scarcity of moles is an indicator of collapsing soil ecosystems, on top of soil erosion and compaction. If so, there’s no doubt the mole is a ‘canary’ for the health of our soils. It’s too serious to ignore and, given that this is the International Year of Soils, there’s a critical need for strong land ethics.

Mole hills in the Monadhliaths

Mole hills in the Monadhliaths