Caterpillar: "Dorsum marked with 10-11 white, intersegmental white spots and paired red setal warts on T1-A9", head black, sides blue-gray. (1)
Pupa: shiny dark brown with erect yellow setae (hairs)
Canada and northeastern US. Bugguide reports it from western states and provinces, too.
Introduced from Europe in 1920.
Caterpillars eat aspen, poplar (both Populus spp.) and willow (Salix)
Overwinters as third instar under bark. Goes through seven instars before pupating in a thin cocoon between leaves or on bark.