I wish I had this when I was a kid. When I was little our dog had puppies and my dad made a house and penned them in the back yard. I’d kill over 100 flies a night and it didn’t do much.
Get a soda cup - the kind that has an X cut in the lid so a straw can be inserted. Discard the straw, if present.
Make sure that the flaps of the X are pushed in, but not all the way.
Put a small piece of fruit in the cup.
That’s it!
If you want to kill the flies anyway, put liquid in the bottom so they will drown, or put the cup in the freezer for a while. (I once tried to release some fruit flies in winter; they only lasted a few seconds.)
According to my dad, in rural India in the 50s, people would make a torch out of discarded coconut fibre and hold it up at night - instant insect roast, and local stray dogs would come running to crunch up the remains like Cheetos