Probably the same reason as mine, Lyn, and I think it's probably because the compost isn't heating up enough to kill off any insect larvae, but I'm not sure. Perhaps someone else will have a solution...Annie

I have tiny flies in mine too, I 'm faid I can't help. Jackie

they are part of the chain of decomposers. there is nothing to worry about. The eggs hatch and the larva munch the plant material. they then provide food for other creatures. I find allsorts of animals in mine from centripedes to false scorpions, spiders, nematode worms and a whole host of other critters. Not to mention true worms too.

I have lots of lovely very thin red worms in mine. If you have ants though its because the compost is too dry.

I usually have tiny flies in my compost heap. They're fruit flies that hatch from eggs on fruit skins like banana peel. They're harmless and as Seaburngirl says, take part in the decomposition cycle.