Fly larva, whether common house, Black Solder, or one of the others, need a very moist environment to exist. If the environment they are living in gets too dry they die, adn the environment they need to live in is too wet for a good compost pile and that is why having fly larva of any kind in a compost pile is not a good thing. The environment they need to live is too wet for your compost pile.

The larvae probably hatched into flies and flew away.

BSF larvae eat raw organic matter and worms eat BSF larvae poop. BSF larvae and worms are a great tag team in the compost.

You probably disturbed them by dumping the bin and such. They may simply have crawled away to find a dry place to pupate. BSF larva are great to have in a bin as they tend to exude a chemical that can to some extent keep other flys away. If you have an active population of BSF in your area, then as you and stuff to your bin, they will probably come lay more eggs in it. If you are trying for actively hot compost then BSF may be a sign that things are a little too wet but if things are not smelling bad, then I wouldn't sweat it, let em happen.

Here is a link that might be useful: My Garden

I have never been near a compost pile that had fly larva of any kind that smelled pleasant, because to have those fly larva, maggots, the compost needs to be so wet that it is in anaerobic digestion.
In my some 45 years of making compost I have not had any good experience with compost that had maggots crawling around it. They are not good for compost.

Anyone is welcome to come to my house and smell my bin.
Its on the dry side, and full of insects. I get BSF larvae and silverfish. They eat and poop and leave me a nice compost when they are gone. My bin is not anaerobic nor does it smell and it isn't too wet either.

Kelly Slocum a vermiculture expert had a great informative post about BSF larvae awhile back. I'll see if I can find a link. There are many myths about the presence of BSF in compost. One of them is the moisture myth.

Here is a link that might be useful: Informative post about BSF

Thank you for the helpful and informative link, JPW. :)

I miss KellyS.

All the best,
-Patrick

my bin was dry and for sure it seems to be doing well especially after the whole BSF larvae episode. well thanks for the helpful information