This a Yellow Jacket, from the Genus Vespula (Click the Pic to enlarge). I noticed it this week chewing on my fence presumably to make pulp for nest building. I don't usually pay much attention to my fence, so I was surprised to see these markings covering my entire fence, left by these busy insects. Here is some good information on the yellow jacket's habits and life cycle.
Also here is a short video of the yellow jacket chewing my fence (mpg,4 sec,1.6 mb), and a longer video can be found here.
Don't forget to check out Modulator's Friday Ark and the Circus of the Spineless at Milk River Blog .