Question 1: "How can we trap them?"
Putting old fruit in a container and then trying to lid it and take them out, doesn't work. If you'll notice, they tend to walk around the rim of the container most of the time and once the lid comes close, they fly away. I had put a small bit of wine in a glass close by for him to see that some will go there and drown. But the BEST trap I found is to put plastic wrap tightly over a bowl with some fruit in it and poke fork holes. It's amazing how many get trapped in one day! and the sound when you get close is eerie! He empties it after several days in the compost and starts over.
Question 2: "What's their life cycle? Are we just breeding them?"
Years ago when schooling the kids we did do a fruit fly experiment, but I forget the facts. I knew they have a short life span, but didn't think they grow overnight! I LOVE the internet! Diagrams, facts, tips, videos, virtual tours ... I took a movie with my little cannon elf. This is the first time trying to post my own movies! You'll notice the flies still walking the edge, so they never get back to the holes to fly out.