I haven't ever worried about it, here are my general guidelines:
- plenty of cardboard and pulp egg cartons, the structure gives worms places to escape to and lay egg capsules.
- no citrus or fresh pineapple.
- no tropical fruit skins (pesticides).
- no dairy or meat.
- nothing too oily
- worms never eat anything that is alive, including seeds.
- best to chop up or dry out fresh veggies, because many will just start growing and never get eaten
- watch your worms, if they are climbing out something isn't right.
- add ground up egg shells, they provide calcium and a buffer against organic acid buildup.
- make sure you have plenty of air, and not too much water, drain holes in the bottom are a must.
- most pungent/strong food has herbs and spices that are antihelmetic... Don't add any dried wormwood, rosemary, etc.
- no hair.
The worst horror stories I have heard involve either pesticides from banana peels or ant invasions.
The old timer that sold me my worms has been vermicomposting for 30 years, and always makes sure his worms have access to alfalfa pellets, because, he claims, the worms can eat them directly without first being digested by fungi... I don't know if it is true.