I am looking at composting earthworms, which he needs for producing vermicompost. I've seen a number if sites that say they're 'high' in B12 or that they are a 'good source', and apparently they add B12 to the soil, but the sources I've seen give no actual values. The only source I've found that gave numbers listed "Earthworms" as if it was one species, with a value of N/A for B12, yet distinguished between different varieties of fly larvae. I have not been able to access scientific papers as I lack the funds to join the databases or buy the articles outright.
I am primarily looking at Eisenia fetida (previously foetida) (red wigglers), but Eisenia andrei (red tiger), Lumbricus rubellus (red worms), Perionyx excavatus (blue worms), Eudrilius eugeniae (African nightcrawlers), or Eisenia hortensis (European nightcrawlers) would also work. Even an educated guess would give me something to go on.
ETA: Spoilers in the comments