A couple of days ago was a particularly buggy day.  We get this a couple times a year in our neighborhood: you go outside to enjoy a cool, sunny afternoon outside and are suddenly chased back inside by a literal swarm of gnats and mosquitoes.  It's like a very tiny, way less dangerous, way more annoying version of The Birds.

I haven't ever figured out what brings them out in droves like that, but the spiders love it.  Those aren't raindrops you see on that spider web above, they're bugs. 

Can't see it?

Take a closer look: