Corn cobs

From WormWiki

Corn cobs break down very slowly. They do not decompose very quickly, therefore, they have no microbes on them for the worms to eat. The only problem with putting them in your bin is that they will be around for a while. You may want to compost them another way if you have that option. If you want to put them in your bin, consider chopping or shredding them in some way. Alternatively, you can just pick them out as you harvest your bin, and put them back in to break down further.