Never been called a plethera
Actually I have not done this, just imagine it would work.
No I don't mind at all. Judging from the BSFL I have had, you could do a good screening with 1/8" or 3/16" hardware cloth. Make a frame out of 1" x 4" lumber to fit just in the top of one of your bins and attach hardware cloth to the bottom with tacks or staples. You could scoop the larvae out of the working bin into the screen box or just pour some in and shake the little ones through and toss the bigger ones to the chicks or refrigerate till you're ready to use them.
As far as feeding their castings to your worms, you would have to do a total bin cleanout by stopping the entry of new eggs and letting all the larvae in that bin grow to size before screening. 100lbs of food scraps = only five pounds of BSFL castings so it may take awhile to make it worth harvesting them.
A word about the little bitty larvae. Regardless of what you read, they can crawl up a verticle plastic wall if there is any condensation at all, even the big ones can and sometimes they carry their own moisture if the bin is especially wet. Don't be surprised if you see this. You can keep them contained with a lid but it needs good ventilation.
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