I noticed a couple of these Baltimore checkerspot larvae along a trail in Larose Forest. One year, this trail was full of Baltimore checkerspot butterflies, beautiful in their orange,black and white colours. To see what this spiky little guy turns into: http://www.pbase.com/laroseforest/image/113485831.
These caterpillars are very closely associated with turtlehead plants and when the caterpillars are small you can find them clustered together in silken webs attached to turtleheads: http://www.pbase.com/laroseforest/image/113483759