Hmm.. well I was going to guess nearly mature black soldier fly larvae, but that's not what you think they are. I often don't know I have these until the bin gets hot, then they start running for their lives and that's when I see them.

The medusa description sounds like BSF larvae. They tend to make a creepy crawling mass of grossness... I would mix well, maybe add some browns to cover them up, they will be gone soon....

Thanks gnomey and joepyeweed. I am going to hope they are BSF larvae and add some more browns (aren't fall leaves wonderful!) to cover them up. I am not very squeamish but these are quite creepy...horror film-like even. They are definitely a creepy mass.

I had a compost bin that was really short on carbons that I found what sounds like the same thing you had. Thank goodness the leaves have started falling. I transferred from the really wet bin to my other bin and layered leaves between them. I'm not sure what they were but if they like it wet then they will either move on or get decomposed and added to my mix. I'm sure they were just doing their job of breaking stuff down in a really wet pile.

Many people, I think mistaking the Black soldier Fly for the Black Soldier Beetle, say these grubs are beneficial. However, since the BSF as an adult does little except mate and produce eggs that become the maggots and these maggots need a pretty moist environment to hatch and grow they arfe an indication that your compost is too wet to properly compost, and a oo wet compost pile will not have the active thermophilic bacteria that actually generate the heat you are looking for.

IME, my pile is on the dry side. I still get the occaisional BSF larvae mass of oozing grossness. The moisture or the larvae are not necessarily a problem.

I notice the bsf larvae when my compost cools down, not necessarily when it is all that wet because mine never is all that wet. I keep it borderline too dry because I pretty much fear a slimy mess. When I see them, I add more materials, heavy on the greens but balanced, give it a good turn. The next day I usually see them running for their lives because it gets to hot for them. They aren't bad for your compost, but if you want to get rid of them then get your pile really hot.