My dog is deathly scared of flies???

It's exactly as the title says. Last summer we discovered, that he is really scared of wasps and tries to hide from them. Today, a FLY got into the apartment and now he has been SHIVERING, hiding under the bed or on us. Is there any way we can train this, as this is not exactly something you can avoid? So far, we've tried to not comfort him too much as to not affirm his fears or anything. Please help :')