I bought this unit primarily for killing flies, however they are just not attracted to it at all.  It doesn't do much in the daytime but at night it comes alive.  It does a good job attracting all kinds of insects that buzz around at night.  The cats in the backyard seem to love this thing as they gather around it and wait for falling insects.  To them it's like sitting around a barbecue, all they have to do is to wait for a tasty treat to fall down.  It's funny to see them sit under it all night long. :-)