Northern Prairie Wildlife Research Center
Extremely variable in color, from green or creamy white to black, sometimes marked with orange-red above abdominal spiracles. Oblique lines pass along base of subdorsal scoli, especially on fifth to seventh abdominal segments. Spines usually light colored with black setae at tips. Dorsal spines on second thoracic segment roughly similar in size and color to those behind. In question mark, dorsal spines on second thoracic segment tend to be more developed and darker than those that follow, especially those of abdominal segments. Head of comma with more pronounced and denser projections than that of question mark. Food: elms, hops, and nettles. Caterpillar: May to October, 3 generations in South; 2 in North.