The spicebush swallowtail has a wingspan of three and ﬁve-eighths to four and seven-eighths inches. Its body is mostly black. The upperside of the hindwing is blue-green (male) or iridescent blue (female) in appearance. The underside of the hindwing has orange spots and a rounded extension from the back edge. The spicebush swallowtail caterpillar is dark green on the back becoming whiter on the sides. This smooth larva has two, large, round black spots with orange or yellow edges near the head followed by four lines of blue spots with black edges. When disturbed, the caterpillar can extend a scent gland that gives off a bad-smelling substance.
The spicebush swallowtail may be found statewide in Illinois. It ﬂies low to the ground and ﬂutters slowly when feeding on ﬂower nectar. The caterpillar feeds on spicebush and sassafras. This insect overwinters in the pupa stage, which is usually attached to vegetation.