They look like mites to me. It is part of a composting system. Their number depends on the condition of the bin. Too wet, too much food and/or too acidic is their favourite environment. Sprinkle some crushed egg shell and add shredded paper product on top should reduce their numbers.

I also have the worm factory (360), and had a bloom of mites. What got mine under control was drying it out some. I added lots of dry paper and picked up each tray and turned it so they weren't nested for a couple of days, and the same thing with the lid-turned it so the corners were open. That only helps if its a case of too wet, though.