Yesterday Duncan at http://bencruachan.org/blog/ posted a photo of a tiny snail on an orchid - he only spotted the snail when he looked at his photos on the computer monitor. And check out this one by Pamela on August 17 at http://thomasburg-walks.blogspot.com/. There's a lovely photo of a yellow spider that you can only see because it is eating a fly.
I've done the same thing. Missed seeing what is perfectly obvious when I see the photo on screen. I wonder sometimes if I'm blind to detail or concentrating too much on the technicalities of focus, shutter speed or in too much of a hurry. It's a nice surprise when it happens though. And an even better surprise is when the insect is actually in focus, accidentally. Here are some of my camouflaged invertebrates.