What do worms in a bin eat? When thinking of what to feed worms, it's easier to think about what not to feed worms.
Don't Feed:Greasy foods
Alcoholic food or beverages
Animal products (meat, cheese, eggs, and any meat eaters' feces)
Eisenia fetida are manure worms. Their very favorite food is poop from other animals, But in a bin, manure does two things- 1) it can really stink, and 2) it can heat up and kill the worms, or at least make them very miserable. A stinky bin will just make you and your family very miserable (though the worms don't care).
I feed my worms a combination of poop from the house rabbits and kitchen scraps- finely chopped vegetable trimmings, cooked grains, stale bread. There's a food chain regarding who gets fed what and when in the house; saint-husband and I get first dibs. Bunnies get second dibs (vegetables only). Worms get whatever is left over. If I had chickens (*sigh*), they would be fed between the buns and the worms. I'd feed chicken poop to the worms, too, but only after it was pre-composted. Chicken poop is very high in ammonia and in concentrated amounts is dangerous in a bin. It stinks to high heaven, too.
When it comes to feeding the bunny poop, I have found that if I feed in very fine layers- say, a little every day and only on the surface- it neither stinks nor heats up. I feed whatever is in my buns' litter boxes every day, and it's gone in 24 hours. The bunny poop will make absolutely outstanding castings.
NEVER feed bin worms human, cat, or dog poop. It is full of pathogens and can make potentially dangerous castings. Worms in the wild will obviously eat any kind of poop that happens to be on the ground, but they have helpers in the weather, microscopic soil critters, UV, and other animals. In nature there is no waste. In human-controlled environments that's another matter entirely.
My worms also get fed nearly all our household junk mail (except for glossy paper- worms can't process it well and the inks can be poisonous). I use it as bedding in combination with my neighbors' newspapers.
So, what's the difference between bedding and food? Not much to the worms. In a bin, damp, fluffy, pre-soaked bedding is kept on top of the food and worms. It helps draw the worms to the surface since they are moisture-loving creatures. It helps keep the bin cool and aerated. It also controls odors if a new worm farmer overfeeds the bin. And ALL new worm farmers overfeed their bins, despite many well-published warnings not to do so. I was certainly guilty of it.
Eventually, the damp bedding gets eaten, too. My worm's castings are fairly light in color because of the paper. The nutrient balance in the finished castings is likely still good, though, because of the vegetable trimmings and, most of all, the fabulous bunny poop.
Come May or so, I'll be sending my first castings off to a lab for testing. It's required for resale of "soil amendments". Perhaps by June, I'll be selling my first castings at our local farmer's market.