For large jobs of sifting worms from castings or compost I use my Texas Worm Harvester, but for smaller jobs I have built a small box sifter. With some scrap materials, and the left over 1/4 inch wire mesh I had I put together this sifter. I have also seen where other worm farmers use 1/8 inch screen, for my use I have found the 1/4 inch to do just fine. Separating worms from castings using this or the harvester method is the first step I take and removes most of the worms are course unprocessed organic matter. I do spend time picking out tiny worms and eggs, but losing a few is not a big deal. Here is a picture of a tiny hatchling that I found while harvesting castings. As you can see, or maybe not, these little guys are hard to find. This little thread of a worm was wiggling which made him easier to see.
Texas Jumpers 