Northern Prairie Wildlife Research Center
Green, brown, or tan twig mimic with conspicuous reddish or darkened thoracic and abdominal swellings. Head reddish brown, flattened and sloping; vertex somewhat lobed to either side, lobes often bearing pale triangular area, widest behind. Second thoracic segment conspicuously swollen. Abdomen: second segment with small subspiracular and ventral warts; third bearing conspicuous lateral and dorsal swellings, and sixth with dorsal warts; subtle longitudinal wrinkle forward of spiracle. Straw besma (B. endropiaria) has warts like those of oak besma but tending to be greener; (especially on maple). Food: many forest trees including conifers. Caterpillar: May to October; 2 generations in North.