Rotten food!
You can see the green lynx spider's prey in
this photograph. You see all the little blurry things on the dead
wasp? Those are little tiny flies. There were really buzzing all
over the dead wasp. I think that the spider pulled that wasp out of a
pitcher, and so the wasp was covered with putrefying juices. Hence the
worshipful flies. This is an interesting case of kleptoparasitism by
the spider.