I imagine in soil with any amount of rocks at all, ground penetrating radar and seismology are going to detect the rocks better than they would worms. I wonder if the worms make enough "noise" or vibration to be detected passively? I imagine not, but that seems like it has at least as much potential as the active detection methods for this case.
It's like a snake worm thing.
https://en.wikipedia.org/wiki/Caecilian
And apparently they produce something like milk to feed their young. Wild!
https://en.wikipedia.org/wiki/Caecilian#Milk_provisioning
with that capitalization i had 200ms of my brain going "what part of the bible is that"