So I finally found a reliable source for houseflies. I got a bunch of pupae in 2 sizes, fly food and containers, and hatched them out. I was told to stick the flies in the fridge for 15 minutes before using them because the cold slows them down to a crawl. That worked like a charm - dusting and introducing them to the frog enclosures were not a problem at all. The fun came later, when the flies thawed out and regained their senses.
The thing about flies is that...they can fly - and incredibly well at that. My frogs (3 red eyes, 4 clowns, 1 hourglass, 1 pacific chorus) had mixed results catching them, although they got a much needed workout from trying. In the night I could hear them battering against the glass, no doubt trying to land an elusive meal. They got a few, but many flies were left buzzing around the ceiling of the vivariums. This is a problem, because every time I need to open the door of the tanks to do something like change the water or spot clean, flies would escape. And they are diabolical when it comes to identifying escape opportunities. It didn't help matters that two of my tanks had a little space between the door panel and the bumper hinge. That space was just wide enough for the smaller flies to get out. I've since plugged the space, but not before an untold number of them got loose. So as of last night we had at least a dozen flies at large in the house, which made dinnertime more interesting to say the least. The family is threatening to either disown me and or have me disown my frog hobby, maybe both
Now anyone who has ever kept large numbers of crickets knows that escapes are a fact of life. The good thing about crickets is that 1: they seek out the nearest dark crevice and disappear, 2: they don't invite themselves to your smorgasbord, and 3: they can't fly. Tracking down and swatting escaped houseflies is a pain in the backside. They won't leave the house through the windows because it's 30 degrees out. As I'm writing this, there are still flies circling inside the tanks. I dare not open them until I've sprayed them down and the water droplets keep the flies grounded.
If you can find a way to make it work (tolerant parents, spouses, roomies, what have you, are a must), houseflies are actually a good change of pace in food source. Frogs find flying insects irresistible and their hyperactivity will draw the attention of even the most sedentary individuals. Pursuing them should stimulate activity levels in frogs, which can only be a good thing. I would, however make sure that the vivarium is escape proof first. It would also help if the tank was densely filled with foliage, right up to the ceiling so that no matter where the flies go, they're within a leap away from the frogs or closer. Having frogs that are at least semi-active and alert helps too. My red eyes did not appear up to the task.
A few miscellaneous points: Flies are not particularly nutritious and would not be a good staple food. They should be gutloaded and dusted. Handling a 16 oz. cup filled with hundreds of buzzing houseflies is not for the squeamish. Do whatever business you have with them in a closed bathroom, swatter handy in case of mass escape. Unhatched pupae can be stored in the refrigerator for months. Hatched flies last several weeks with proper care.