Unless you already have frogs or day geckos or something that will eat the fruit flies, then they're probably not worth the effort. They're just so small they won't be enough for collareds. Mine are nearly two months old now and will still eat phoenix worms, though. They like the (very) occasional butterworm. And my nephew brings me wild grasshoppers for a dime apiece - the collareds LOVE those!
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Torey
Eugene, Oregon, USA
1.1.5 Saharan Uros (Joe, Arthur, Waddles, Stilts, Hitch, Lefty, and Skywalker)
3.0 Mali Uros (Spike, Turtle, and Tank)
1.1 Ornate Uros (Scuttlebutt and Shazzbot)
1.3 Collared Lizards (Ripcord, Thiamine, Riboflavin, and Niacin)
2.0 Green Anoles (Bowser and Sprocket)
1.1 Chubby Housecats (Roscolux and Jenny)