Larger than the other Rosaceae-feeding species as mature larvae, ultronia can usually be told by its size, solid black band around the top/sides of the head capsule (other species usually not as solid and/or with red infiltrating), typically quite tall horn on segment A5, prominent black venter spots. Ground color often grayish brown, but variable. Larvae of ultronia specialize on cherries, which are shunned by the other Rosaceae-feeders, and a Catocala larva feeding on either of the two widespread North American cherries (Prunus serotina, Prunus pensylvanica) is almost certain to yield an ultronia.