I use a stick and a small hand held net. If you put the point of the stick up higher than the branches of the bushes around where they are they typically land on the end of it then you lower it slowly and place the net above them because they tend to take off like a helicopter ... there you go...
They will eat any thing lol but I would only use what I would typically use to gutload crickets and roaches. Fruits are fine too. I honestly have thousands in my bucket right now so many that the little anoles hang out to get free hand outs as well as toads and frogs.
I use just veggies that I would have given to crickets or roaches as gut load and no meat or waste products so I would have to assume that it would be. Pilotman if you are "growing your own" then yes they are gut loaded by what you use to attract the adult flys to lay their eggs in and then the...
If you live in an area where Black Solider flies are native to you can start a 5 gallon compost bucket with veggies in it and you will have an endless supply of them ...until the cold weather kicks in. That's what I did. Buy as Syn stated some chams don't go after them due to lack of movement.
Just a note
Collagen is one of the chief ingredients of gelatin. Collagen is a scleroprotein found in the bone, cartilage and tendons of animals. When the bones or tissues of animals are boiled, collagen yields gelatin.
just my $0.02