What are the differences between composting worms, like the Red Wiggler, and the earthworms you might see outside after a heavy rain, or you might see digging into the soil?
Well, there are 3 types of soil dwelling earthworms; Epigeic, Endogeic, and Anecic.
Anecic Worm Burrow
Anecic (Greek for "Out of the Earth") Earthworms live in deep vertical burrows that can be several feet deep. They are usually the largest, and slowest moving. When it rains, these worms will often come out of their burrows to avoid drowning, and you'll see them dead on concrete because it
disorients them and they aren't able to find ther burrow before the sun comes back out. They are not suitable for a worm composting bin because they prefer to live in very deep burrows, in soil rather than organic matter, and not in very dense populations.
Endogeic (Greek for "Within the Earth") Earthworms live in horizontal branching/networking burrows in the soil. They usually stay in the top 20 inches or so of the soil profile, and feed on the soil itself. They rarely come to the soil surface and so they have little to no pigmentation - they are very pale. They are smaller than anecic worms, but still bigger than epigeic. They are not suitable for a worm composting bin for similar reasons as the Anecic Earthworms.
Epigeic (Greek for "Upon the Earth") Earthworms thrive in pure decomposing organic matter. They do not make burrows, they eat pure organic matter, and they can live in densely populated conditions. These worms are ideal for worm composting for those reasons.
These Epigeic earthworms will not populate soil as well as other types of earthworms. They do not make burrows and naturally only live in the top few inches of a soil profile, but it is possible if there is enough organic matter available for them as they eat organic matter instead of soil itself.
Epigeic Earthworms include the Red Wiggler (Eisenia Fetia/Andrei), European Nightcrawler (Eisenia Hortensis) and the African Nightcrawler (Eudrilus Euginae).