One thing that I tend to always reply when someone asks about worms and compost is this... There are the earthworm types, and there are red wigglers. Our gardens have an essentially sand-silt soil (the
mineral soil aspect), but both the people who owned this
land before us and we ourselves have amended the soil and worked toward developing a reasonable topsoil—going back to the mid 1950s, three owners before us, when the land was cleared of
trees.
We find a lot of the common earthworms and also "nightcrawlers" (like a giant earthworm) in our garden soil.
Then there are the compost worms, the red wigglers. We're using a common three-bin compost containment. Pretty much the same as the one featured in this how-to:
https://backyardfeast.wordpress.com/2011/02/15/how-to-build-the-ultimate-compost-bin/
Because we put a fair amount of green grass clippings into our compost, the piles will heat up. This heating phase breaks down the coarse materials, including the grass but also coarser garden waste, kitchen waste, etc. Then the pile will cool off. Red wiggler worms then show up spontaneously in our compost bins, so it seems evident their eggs are just in the bins.
But when we apply compost that has lots of red wigglers in it to our gardens, after a fairly short while we never run across red wigglers in the garden soil. Even when weeding or digging, we just don't see them. I don't know what happens to them,
but their habitat seems to be in the compost materials so long as these are cool, not hot from bacteria processing the carbon/nitrogen materials. From our practical perspective, the wigglers do a job of further digesting and enriching the compost with their castings.
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