No issues with critters. My bin is a 2’x4’ galvanized water trough, I placed a plywood cover on top. The lid is heals slightly ajar with thin strip of wood. This lets the adults in and the pupae out.
The only issue I have had are a few ants and some spiders. Otherwise the bin is trouble free.
To expand on this:
I feed counter scraps, old fruit and vegetables from the garden, fish carcasses, scrap meat, etc and (dewormer free)dog poop to the bin. Dog poop is the primary feed. I use peat moss as bedding and add crushed lump charcoal to the bin for inoculated bio char.
I’ve had...