If it grew, the worms can likely eat it. Red wigglers eat most things organic including fruit/veggie scraps, bread, coffee grounds/filters, tea bags, grains, plant trimmings, paper, leaves, etc.

Assuming you are raising worms in confinement, there are several things you should avoid feeding them. Any kind of food that is highly acidic, like citrus fruits or rinds, or tomatoes or tomato products, can significantly lower the pH of your worm bin, possibly to a level that is deadly for your worms.

The best thing to feed your worms (and simultaneously the best thing to use for bedding) is manure. However, you should only use the manure of ruminant (plant-eating) species, such as cattle or rabbits. The manure of carnivore (meat-eating) species, such as dogs, cats, and humans, is not as healthy for worms, but the most important thing is, it smells a lot worse than ruminant manure, and you don't want to gag when you are checking your worms.

Crushed egg shells are highly recommended for worm bins because they are a good source of calcium, increase the pH of the bin, and promote reproduction. Plus, if you are growing worms for fishing, the calcium helps to make the skin tougher, which makes it easier to thread a worm onto a fishing hook without the point coming out. However, you should never put raw egg shells in your worm bin. Raw egg shells will have some of the egg white clinging to them, and this could carry diseases that are harmful to your worms. Not to mention, it will stink to high heaven when it rots. If you boil the eggs before peeling them, the peeled shell can be put directly into the bin. But if you do something else with the eggs, such that you crack them open before cooking them, you can boil the empty shells for 5 minutes and they will be fine. One more note about egg shells. Egg shells have a thin, pliable film on the inside. When you crush the shells, this film will come away in sheets or strips. Put this film in your worm bin as well. I have found that worms like to use this film for laying their egg cocoons.

Fats and oils should not be fed to worms. Not only do they lower the pH, they also tend to stink when they rot. You should also avoid all meats and dairy products for the same reason. There is, however, one notable exception to the dairy product ban. If you are planning a fishing trip, 3-4 days before your trip, you can set aside enough worms for your trip in a separate container and feed them milk or, better yet, powdered milk. This will boost their calcium and toughen their skin. But you can't use that bedding anymore - throw it away.

You should also avoid any kind of "processed" foods, as these usually contain salt and other additives that will not be consumed by the worms, and thus will accumulate in your bin.

If you're growing worms at home, and don't have access to rabbit manure (or just don't want to smell it), the best thing to feed your worms is regular corn meal. Just make sure you get the kind that doesn't have salt and other additives.

If you want to save money on feed, you can feed your worms your kitchen waste (but pay attention to the "don't's" above). Any kind of raw fruits and vegetables (except the acidic ones) are great. But you want to chop them up into small bits, like a quarter-inch or smaller, so they will decompose more quickly. I like to put potato peels in my bin, but there's a slight problem with that. Potatoes reproduce themselves from "eyes" located on the peel, and often these eyes will sprout in your bin, and you have potato plants growing in your worm bin. If you get this, you can pull out the plants by the root, or just bury them in the bedding, where they too will be eaten by the worms.

Oh, I almost forgot. Watermelon! If you have any leftover watermelon, that would be excellent for worm food. The rind is fine too, but the red, fleshy part that humans eat is fantastic. I put about a pound of it in my bin one day and two weeks later, I had literally millions of baby worms. But watermelon is slightly acidic. It's probably not enough to kill your worms, but to be on the safe side, you might put a few egg shells in with the watermelon. Also, keep in mind that watermelon is about 95% water, so your bedding might get a little soggy. So don't add any additional water for a while, or you might drown your worms.

And though you didn't ask about it, that brings me to another important point. Worms need their bedding to be moist, but not wet. What I have read says that if you scoop out a handful of bedding and squeeze it tightly, you shouldn't get more than a few drops of liquid dripping out. In my experience, more than a few drops is okay, but you definitely don't want water streaming out when you squeeze the bedding.

And as for bedding, I use peat moss, but there are lots of things that will work. As mentioned before, ruminant manure is great for both bedding and food. Crushed leaves are also good. Some people use shredded newspaper (I don't know if it's important or not, but I've been told to avoid any color pictures from the newspaper). Some experts recommend adding a small amount of sand or other gritty soil to your bedding, because worms need something gritty to help digest their food. However, you should never use a sandy, gritty, or clayey soil for the majority of your bedding. Worms need a lot of organic matter in their bedding.

There are lots of resources online for tips on how to raise worms.

To add on to this very well written info, one of the general rules for deciding what or what not to feed you worms is: do not put anything into the bin that if rubbed over an open cut on your skin would irritate it. Wigglys have a very thin sensitive skin through which they breathe, so things like onion, garlic, ginger, lemon or limes (even though organic) would irritate their skin greatly. Also, adding properly prepared crushed egg shells not only helps the PH of the bin, but aids in the worms' digestion just as sand does with birds. For my own bin at home I just chop up most of my scraps by hand, but when feeding many bins as I do at our school, I find it helpful to use a large food processor to grind the food into small pieces when I have a lot of scraps to prepare. Also, it's one way to make sure the food you give them is not in big pieces that are too big. Many people think that a worm bin will smell badly, but if you always keep the worms and their food completely covered as mentioned above, your bin should smell like fresh soil when opened. One other neat hint, if using newspaper as bedding/food for your bin, putting it through a shredder first, makes the composting happen MUCH more quickly. For years I used to have the children rip the newspapers into small strips, but the shredder method is much more effective! It also makes for a more airy topping that the worms can breathe through.

Earthworms extract nutrients from the decomposing vegetation, such as rotting leaves, and other organic matter, such as dead animals, from the dirt that they swallow as they tunnel through the ground.

Mostly Dirt. But not only dirt, but mostly the nutrients from rotting plant matter in the dirt.
Dirt.