Viceroy

Description:

Its wings feature an orange and black pattern, and over most of its range it is a Müllerian mimic with the monarch butterfly (Danaus plexippus). The viceroy's wingspan is between 53 and 81 mm. It can be distinguished from the monarch by its smaller size and the postmedian black line that runs across the veins on the hindwing. — Wikipedia

Notes:

The caterpillar feeds on trees in the willow family Salicaceae, including willows (Salix), and poplars and cottonwoods (Populus). The caterpillars sequester the salicylic acid in their bodies, which makes them bitter, and upsets predators' stomachs. As further protection, the caterpillars, as well as their chrysalis stage, resemble bird droppings. Adults are strictly diurnal, flying preferentially in the late morning and early afternoon. Adult viceroys nectar on milkweeds, thistles and other common flowers. — Wikipedia