My theory on the camo of these spiders is that it allowed this one to catch a bee. I posted this on Naturescapes and someone commented that the bee can see the spiders just fine, it was just too hungry to pass landing on the plant. I'm sceptical, as there were plenty of Yarrow around without spiders on them that the bee could have landed on, but maybe the person knows what they're talking about. Anyway, it makes a good story.