Just an observation. I was digging some Parnips up at the weekend and noticed small pockets of very dark crumbly soil, about 15-20cm deep, in amongst the heavy, wet clay soil. The soil has been no-dig for 5 years but clearly the worms have been at work taking the down the compost that I have been applying to the soil surface. I was surprised at the depth and quantity of these pockets of compost.
I love to hear that and worms amaze me too how they can build fertility, improving both drainage and moisture retention at the same time. Their activities are mostly invisible so I always enjoy an occasional look, usually when digging parsnips as you say.
I was surprised during the slightly milder spell that we had between snow that there were quite a few on the surface mating, I had always assumed they waited till it was warmer, but perhaps it has more to do with nutrients and moisture levels?