Northern Prairie Wildlife Research Center
Highly variable, brown or black with irregular, pale dorsal saddle and humped eighth abdominal segment. Third thoracic segment somewhat swollen forming hump; first and eighth abdominal segments also humped. Head brown with curving black band to either side, or entirely black. Dorsal saddle confined to abdomen, reaching almost to spiracle on fourth segment. Black spiracular stripe on abdomen broadening to rear. Eighth abdominal segment with whitish spot above spiracle. Food: evidently grazing algal layers off of tree bark. Caterpillar: June to October; 2 or more generations in South, 1 in North.