The caterpillar above is the larval form of Large Yellow Underwing (Noctua pronuba). I found it as it was walking across a bicycle path in Donaldson Park yesterday morning.
The Large Yellow Underwing moth is a relatively recent addition to North American lepidoptera. The species is native to Europe and was introduced to North America via Nova Scotia in 1979. Since that time, the species has spread across the continent, and it seems to be one of the more common large moths in this area. I have seen adults frequently at UV lights at night. These moths tend to flutter around and not settle down. This would not be so bad except that it often spooks some of the other, more docile moths as I try to photo them on the sheet. Above is a photo of an adult from August 2010.