Thanks, Tony. I'll look around the property for stuff like that. From what I've read, unremoved lawn clippings and dead leaves in flowerbeds can contribute to the problem, so I might work on that too. There's also a strip of land behind the row of houses on my street that's a common area. I don't know who is responsible for it, but I suspect the answer is "nobody." Well, that area starts right behind my fence, and I only noticed recently that there's a roughly 15sqft area of dead leaves piled about 6 inches deep. I can't imagine that's a good thing.

I'd hate to hire people to clean up an area that's not even mine, but that might be what I have to do...