I just read a short column in the Guardian about why zebras have stripes. It turns out that zebra striping is geographically coincident with biting flies. That is, the more of an annoyance biting flies are in a particular region the more likely the local members of the horse family will have stripes. While this is merely a correlation study – from what I can tell from the Guardian piece – there is also experimental evidence that flies prefer to land on solid-colored surfaces relative to striped surfaces. So, it is certainly plausible that zebra stripes may simply be a mechanism to avoid fly bites.
Happily, this was a rare example of science journalism that cites the original publication. If you are interested, the study was published by Tim Caro and colleagues and can be found in the April 1st, 2014 edition of Nature Communications.
The fly-free-and-striped photo above is of a shaded walkway in the Missouri Botanical Gardens.