Hi Nifty-Chicken and everybody, I'm Jerry from the black soldier fly blog that Nifty-Chicken linked to. I don't keep chickens, but I'm available to answer any BSF questions you care to ask.
The first point I would like to make is that black soldier flies are not disease carrying pests like house flies. They have a very different life cycle that results in their being relatively pathogen free. No animal can claim to be perfectly safe to handle, but there is no evidence indicating that BSF are vectors of human or bird pathogens.
The prepupal larvae, the ones that are almost black, are the cleanest larval stage. That is the final stage before pupation. In their transition to the final larval stage they purge their guts, their mouth changes into a climbing hook, and they excrete an antibiotic to protect themselves from infection during pupation. I still wash my hands when I handle prepupal larvae, but I believe they are as clean as your average shopping cart handle. Maybe cleaner. Probably cleaner. :|
There has been interesting research about feeding BSF larvae to poultry and other animals.
Here's a short article.
edit: A couple more quick things...
I'm not at all offended if you think my beloved BSF larvae are disgusting, I once felt the same way. Most of us are taught that flies are nasty creatures, and in a sense this is true, at least of many flies. House flies are associated with 277 disease causing organisms so the feeling is often justified.
I know I'm new here, but I'll ask a favor anyway. It would be very helpful if anyone who has observed black soldier flies in their area would inform me of it. I'm frequently asked by people all over the country if BSF are found in their areas. The data I have found is very general so usually I can't answer with any authority. I'm going to start a page on my blog with a list of BSF sightings to help people who are considering starting a colony. The county you saw them in would be sufficient unless you wish to be more specific. Thanks!