It has zapped hundreds of flies, gnats, moths and who knows what else this summer.  We don't have mosquitoes here in the desert, or it would most likely do a number on them, too.  Very pleased!  I also got the indoor Aspectek 20W zapper and put it by the back sliding door, so it got anything the outside one didn't.  We've had a very pleasant bug-free spring, summer and fall.