We get lots of folks who are worried that their composting worms are skinnier than when they received them.
A vermicomposting environment is a different, often less protein-rich environment than a vermiculture environment where worms are bred for the purpose of sale. The worms in our own bins are quite small as well to be honest.
If the worms are consuming the waste and appear to be reproducing, then there's likely nothing wrong with what's going on in the bin!
If you want to try fattening your worms, you could purchase some of our Urban Worm Chow which is also part of our Worm Success Bundle.