I will be using the European crawlers based on the fact that they are good for composting. Meaning they are more likely to remain in or close to the bin. Not sure of their hardiness, I'll have to see about that.
The bin is not sealed, there is no bottom. The compost sits directly on the ground. Adding mostly leaf liter will keep it loose, allowing for drainage and prevent it from staying too wet. The worms will migrate down into the soil in colder temps but, in my experience, return once it warms up. The compost sort of insulates the ground directly below, so here in Texas, they won't go far. Never really gets that cold for that long.
My thought, as it relates to the original post, is that having the bin may help establish a permanent worm population in the native soils as well. As they move through and condition the soil, they will eventually move further from the bin as their numbers increase and soil condition improves. No idea how long that would take. Could be too long to be practical for that purpose but having a bait source close to the pond is the reason I'm doing it.
