The Boxelder Bug, Boisea trivittata, a rather good-looking bug if I do say so myself. I found myself along the municipal pier at Huron, Ohio, the other day and ran into a boatload of the little critters.
I'm not sure what nasty juices create toxicity in Boxelder Bugs, but apparently they are foul to eat.
Box-elder Bugs tap sap from the trees, and live most of their lives in and around them.
This behavior is what gives the bugs a bad name - they gather en masse seeking sheltered hibernation spots as the weather turns cold in late fall. Sometimes, their favored spots are on people's houses and this irks the homeowner.
Fortunately, at least for the bugs, this swarm was far from any dwellings and those that saw them rather seemed to enjoy the spectacle.