Free soil engineering
Why Are Earthworms Useful?
Worms eat dead leaves, mix the soil and drill it full of air and drainage.
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Step 1 of 5
They eat dead plant matter.
Without worms the leaves would simply stay where they landed Worms pull fallen leaves down into their burrows and eat them along with soil. Without them, dead leaves would pile up for years.
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Step 2 of 5
What comes out is better than what went in.
Worm castings are richer in usable nitrogen and phosphorus than the surrounding soil. The worm concentrates plant nutrients as it digests.
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Step 3 of 5
Their tunnels let air and water in.
Burrows give rain somewhere to drain and roots somewhere to breathe. Compacted soil without worms waterlogs and suffocates roots.
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Step 4 of 5
They mix the layers.
By constantly moving between surface and depth, worms carry organic matter down and mineral soil up. It is slow, continuous ploughing.
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Step 5 of 5
There can be enormous numbers of them.
Good pasture may hold hundreds of worms per square metre — sometimes weighing more, per hectare, than the livestock grazing above.
Darwin spent his last years studying worms and concluded they had ploughed essentially every field in England.
The short version
Worms eat dead matter, enrich it, tunnel the soil for air and water, and continuously mix its layers.
Try it yourself
Compare soil under a long-undisturbed hedge with a compacted path. The worm-worked soil crumbles; the path does not.