In the summer of 2012 i grew cucumbers in a pot on my second-floor deck, with the vines being trained along a brick wall (the black landscaping fabric rolled up at the bottom of the image is for shading the vines on hot days, since the west facing wall can heat up too much for cucumbers). On the same shelf was a compost bucket (far right) which attracted fruit flies and other insects. Robber flies frequented the spot, resting on the cucumber leaves while they hunted fruit flies.
There are also a lot of zebra spiders (Salticus scenicus) on the deck, and especially on the brick wall. While the hover flies hunted, a zebra spider snuck up on a robber fly and pounced on it, locking the fly in a death grip and dragging it off to be consumed in safer place.
I always referred to the spider as “jumping spiders”, after the way they walk along and jump over obstacles or jump away when threatened, but was set straight by Chris Buddle, arachnologist and prof at McGill University who hosts a great blog on spiders; he has information on the zebra spider and what to do if you find a spider in your fruit. The one pictured at left was hanging out on my wall near a computer monitor and desk lamp, both of which attracted other insects that could be hunted.