Dave

A curious thing about flies (and other daytime flying insects) is that
they will usually fly towards the most light. So lots of bug traps work
by drawing the flies in through a small dark opening (usually by scent)
and then having a bright area above which they will instinctively fly
towards once they're done with the bait. There are hundreds of designs
that use this principle. One of the most elegant I've seen was a sphere
of brass mesh with a flared hole in the bottom that sat on little legs
over the bait dish. Looked like an old time hot air balloon, was nice
enough to be part of the centerpiece on a table and caught yellow
jackets like crazy.

Jim