I've tried to use fly traps with very little success. How many does your trap catch per day?
I'm going to look into Ismat's suggestion for sure!
I posted some of this in another thread but you may find it useful...
My method:
I slam a 32 oz. deli cup over some fresh dog manure swarming with flies. The flies fly up, I quickly lift the cup and slide the lid on. No joke, I catch 15-30 bb flies at a time with this method. I keep going back filling deli cups until I'm set for at least a few days. Works like a charm.
:wub:
I then dip a bamboo skewer into organic unfiltered honey, slip it under the lid and deposit the honey on the underside. You can do this in advance too. I just blow in the opening and the flies stay clear. I feed the flies this way once a day and mist with water once or twice a day. They can last a long time on honey and water. I load them up with good food for at least a day before feeding to my mantids.
MantisPlace House & BB Fly Food works great too if you prefer dry powdered food. For my use the honey, if used sparingly, is a little more convenient.
I keep the cups upside down on a paper towel so the frass doesn't built up in the cup and so any excess water drains out so the flies don't drown.
And that's that. Refrigerate and distribute as needed.
I'm keeping over 30 mantids that feed mainly on flies and this is how I catch all their food. I also catch bumble bees in deli cups and use a net for cabbage butterflies. My yard is only 20'x60' but there are plenty of feeders even in that small area. It helps to have a garden, flowers, and, of course, a dog.
( Hey, you kids! Get off my lawn! That's MY dog poop! > :wheelchair: