I the last few days I have been besieged by small flies in my duck run. They're not like house flies and they're not gnats - somewhere in between. I hose down the gravel every day and put DE down in their straw frequently, so I have no idea why there are flies in there now. But most importantly, how do I get rid of them? Is there something I can use on them that isn't toxic to the ducks? They seem to hang out on the walls and ceiling. BTW my 5 month old Rouen duck Ella has started laying eggs! Three in three days. She seems to have no interest in sitting on them, even though she has a mate and they have been "doing the deed".