"mdk77" wrote in message
But I need to line the compartments with something to hold the flies
in place. I thought of buying sheets of Styrofoam or Velcro and
cutting them to size for each compartment. Or maybe cork, like from a
cork board material. Any ideas on this? What do you think would work
best?

My only caution is that whateve you use has to fit really well or be glued
down, or you'll have a few flies getting under, then a few more, until it's
lifted enough for them to start going from compartment to compartment. It's
a PITA. Use whatever you have the best skills & tools to work with.