Imagine that you are a tasty, tasty fruit fly, full of luscious lipids and useful proteins. Just the sort of meal over which any self-respecting fly predator should salivate.
Now imagine that the predatory spiders incessantly stalking you are, like most spiders, solitary creatures. Spiders, you see, are usually happy to avoid their own kind. They find each other to be rather good eating, after all, so the hermit life tends to be the long life.
What to do?
Well, you can always use an arachnid's rather ironic arachnophobia against itself. That is precisely the defensive strategy of some Rhagoletis fruit flies1. Have a look:
Having trouble seeing the spider? Try the same photograph in black & white:
Now compare with an actual jumping spider:
The visual acuity of spiders is such that their prey can use an optical illusion against them.
That's pretty cool.
1- further reading:
Eisner, T. (1985). A Fly That Mimics Jumping Spiders. Psyche 92: 103-104.
Mather MH, Roitberg DB (1987) A sheep in wolf's clothing: tephritid flies mimic spider predators. Science 236: 308–310.