You're right about the larvae getting through, not such a big deal for my system as they will be regularly drained/rinsed into the compost heap and it's fine with me if they develop there. (fyi everyone else, I use my colony as a rapid food waste reducer then add the resulting bug manure to the compost heap later, larvae as bird food are a positive incidental byproduct as my bluebird houses still aren't up yet)
I like the filter idea, I'll get some next trip to the HW store to try. I take it that the filter isnt clogging?