black flies and compost

elsien

I have a bag of organic vegetable compost that I opened last year and which I stored in my shed over the winter. (Not sure of the type, it's one I won in a competition.)
Gone to use it today and it's crawling with little black fly things. The multipurpose compost appears to be unaffected.
Is it ok to use as it is, (planning to use it outside for growing container veg) or should I do something to kill off the flies first? (Bearing in mind I want to stay organic and not use chemical sprays.)
And why have they taken up home in this bag and not the others?

Sally_A

I wouldn't bother about killing the flies, just check there are no remaining grubs in the soil.which could munch through young seedling roots.