The forewings of underwing moths (genus Catocala) are typically dull tan, brown, or gray with wavy lines that mimic the random patterns of tree bark. Almost all of them have hindwings that are bright orange, red, yellow, or pink, with contrasting bold dark patterns — Missouri examples include the oldwife underwing, C. palaeogama, beloved underwing, C. ilia, darling underwing, C. cara, and joined underwing, C. junctura. Some species, however, have black hindwings — for example, the tearful underwing, C. lachrymosa.
There are more than 60 species of Catocala moths in Missouri, and within these there are an additional 40 named forms and varieties. Thus the markings can vary greatly even within a species, and even experts can have a difficult time telling them all apart. You’re doing well when you can identify an underwing as an underwing!
The caterpillars are semi-loopers, differing from other looping caterpillars (“inchworms”) by possessing the abdominal prolegs that other loopers lack. The caterpillars can be cylindrical or flattened and usually have a mottled, barklike pattern above and humps and warts on the top (dorsal) side. They are strong jumpers that feed at night.
Similar species: In addition to the many Catocala species, a closely related moth in a separate genus also occurs in our state. This is the moon-lined moth (Spiloloma lunilinea). Its forewings match the same general pattern of underwings but each has 4 distinctive dark marks along the leading edge — these occur at fairly regular intervals and at a glance look something like the tic marks along a ruler. Also, it has a dark collar behind the head, and it lacks the brightly colored hindwings usually seen in Catocala moths.