Predators like spiders will use the natural inclinations of other creatures, like bumblebees or in this case a Syrphid fly, to capture a meal. The white body and yellow band across the eyes of the spider blend in perfectly with the flower that has attracted the fly. One curious aspect here, is the odd juxtaposition of sizes – the small spider, the large fly. It has an interesting effect, as though the spider might drop the fly at any moment. (It wouldn’t unless it was done feeding or also possibly if a clumsy photographer overstepped his bounds – but he didn’t!)
There are a lot of angles and lines in this photograph, which made it somewhat difficult to compose; for some reason I find the lines on the fly’s abdomen very distracting. Another thing, I probably would have preferred all the petals out of focus, but having both the spider and fly’s faces in focus superseded that consideration. Moral of the story: keep your eye out, there’s a lot happening on a little flower.