While Neil cultures blue bottles, I have had zero success with it. I buy them online, two bags of 1000, at Jada Bait for $25 shipped. They are waxworm sized, though Tidus has proved he can eat 50 just fine! Supplements stick to them like glue, they wriggle like crazy and are soft bodied. The calcium levels are decent in them too. If you buy them, store them in the fridge and change their substrate to aspen because they are packed in pine. Soft wood oils seem to leave a type of film and smell on them and mine won't touch them. I separate the spikes and rinse in warm water, pat dry and put in a Tupperware bin of clean aspen. They don't need to eat while in the fridge and will last several mos. I've had mine for 4 mos and am just now getting a high rate of pupation. Otherwise when kept cold they really don't change much. Blue bottles are by far my favorite feeder.
I like them better than black soldier fly larvae. Mine seem to have a tough time digesting the skins and have regurg'ed them up hours later still wriggling. Yuck. They don't care for them anymore so I don't buy them.