Excerpt from The Earthworm Farmer's Bible

7. What do Red Wiggler composting earthworms eat? Red Wiggler (Eisenia Foetida) composting earthworms have very small mouths and do not have the greatest teeth. In fact, as mentioned above, they do not have teeth! Thus, even though they can eat almost anything that was once alive, it may take them a long time to do so. For example, if you give them a raw carrot they will not be able to do much with it until the carrot starts to decompose and softens up a bit. On the other hand, earthworms will devourer a soft cooked carrot in a few days. Along the same lines, earthworms love newspaper and can consume large quantities of paper waste in relatively little time; however, they cannot handle paper that is matted together. Thus, you will have to invest in a paper shredder if you plan to feed your earthworms newspaper. Along the same lines, earthworms love cardboard, but cannot consume it efficiently unless it is cut up into very small pieces or has been allowed to rot. Covering a worm bed with wet cardboard is a great idea because it acts as an insulator and provides a moist dark environment ideal for vermiculture. As I said, composting earthworms love the stuff. To clarify this issue, I should point out that earthworms are actually a part of a complex food chain that is found naturally in most soils as well as in the earthworm's bedding. At the bottom of the food chain are microorganisms that we cannot see including, most importantly billions and billions of bacteria that cover and help breakdown all decaying material. The next larger organisms in the food chain are the fungi, protozoa and nematodes who primarily eat the bacteria. The organisms that we can see in a earthworms beddings include spiders, saw bugs and white mites. These invertebrates consume the small organisms below them in the food chain. The composting earthworm lives on the top of this complex ecosystem and can consume all but the largest invertebrates in their environment. Of course, they do consume these larger organisms after they die. All of the creatures in the ecosystem eat each other (from top to bottom) and are in turn eaten by other members of the food chain when they die and decompose. With respect to the earthworms diet, the composting worms are not actually eating the organic waste you give them. Rather, they are eating the various microorganisms that cover the decomposing material in their bedding. The organic material, and inorganic materials like dirt, which are present in the worms bedding are consumed incidentally in the process as they eat the bacteria. As you might expect, particle size is a primary consideration when planning an earthworms diet. While earthworms cannot handle fir limbs or the limbs you gather after pruning your fruit trees, they will make short work of fir sawdust and most other wood products if they have been passed through a shredder before feeding it to them. The rule of thumb here is that the smaller and softer the food particle is the faster the earthworms will be able to devour it and convert it to worm castings. So, what can you feed Earthworms? A lot has been written about what earthworms like and dislike. For example, they are not supposed to like citrus fruit, especially the skins. To the contrary, I have found that my worms love the pulp of an orange and will also consume the rinds as soon as they soften up a bit. Composting earthworms ,however, would not do well if fed nothing but, or primarily, citrus skins or citrus pulp because large quantities of this organic material would make the worm's bedding to acidic. In this respect, everything in moderation applies here as it does with most things in life. Similarly, some authorities on vermiculture recommend that meat products not be added to a worm bin. My experience suggests that composting earthworm love meat of all types, the rottener the better. The meat waste must be buried in the worms bedding, of course, to prevent flies from having access it. However, with this proviso, meat products makes excellent worm feed. This is a particularly important point for home owners since they do not have to go to the trouble of separating meat scraps from the kitchen waste they feed their composting earthworms. With respect to home vermiculture, the only type of kitchen waste that should not be put in a worm bin is large quantities of fatty substances like grease, lard and butter. Small quantities of these products are acceptable and need not be separated from the other table scrapes you feed composting earthworms. With this notable exception, you can feed your Earthworms almost anything from your kitchen, even egg shells!