In Summer, there are always plenty flies around the house. Attracted by the compost heap, flowers, snails that I squished flat, you name it. Many of these flies become food for my African Butterflies, but I also noticed that my Festivums go crazy for them.
Rather than catching them one by one, I built this very effective fly trap. It is made out of a 3l soda bottle with its bottom cut off, one of them cross-stitch plastic thingies from the craft isle, and a zip tie.
I roll the plastic into a funnel, leaving a small, maybe 1" hole on the top. I used small zip ties to "sow" it together, then connected the large zip tie. Cut a slit into the bottle cap and pushed the zip tie through. This way I can hold it by the zip tie, which pulls up the plastic and seals it against the bottle.
Okay, now I go out and slowly lower it over poor, innocent big green flies. Once scared, they have an urge to go up, up, up which brings them to the hole on top that doesn't lead to freedom, but to certain death.
I can catch probably 20+ flies in 5 minutes if there are enough around. Once I am happy or tired of it, the whole contraption goes into the freezer (making sure it doesn't open up accidently... wife doesn't like little frozen dead bodies in the fridge). After a couple of minutes, they don't move anymore and either are thrown into the tank or get stored for future feeding. Helps to keep my ABFs happy in Winter when other insects are scarce.
Just thought I'd share.