I've been battling these things for years. I wait for a nice warm sunny day when they've congregrated on large groups and I splash them with warm sudsy water (I just use dish soap). I found this idea online somewhere and it said the detergent degrades their wings and the water drowns them. All I know is it works, it's harmelss to the environment (I think) and I have a clean deck/house after I hose away all the remenants.

(Inside the house I suck them up with the vacuum or flush them down the toilet)