Actually come to think about it. When I moved into my current home back in
1990, we couldn't find any worms anywhere for 3 years. We blamed it on the
heavy clay soil and the black plastic covering that was placed deep inside
the soil when the house was built in 1980.

We bought worms from the local gardening shop, I even transplanted a white
earthworm I found in another friend's home, and things seem to improve.

Last year I dug an irrigation trench (to drain off water in the courtyard)
and found to my happiness that I had earthworms were deep inside my garden
soil, despite the clay. Hope the silly buggers don't get caught in the
trench.

If I don't find any worms, I'll go and buy some at the gardeningshop again.