These window fly traps are nontoxic (they're made with waterproof paper and sticky glue) and are so easy to use. Just peel them off the white release liner, place the trap on your window, and peel off the big release liner to start catching and trapping bugs.
Promising review: "Earlier this summer, we had a legitimate fly infestation. Maybe 100 flies buzzing around the apartment, seemingly out of nowhere. We tried to kill them all by hand with paper towels. That worked a little, until the next morning when it seemed they were back in force.I bought the traps, put up just one pack of them and BAM! These traps caught them all and I don't know, they seemed to not want to come back after that.I took the traps down a month later or so and no more flies." —D Eisner
Get a 12-pack from Amazon for $9.49.