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.
Habitat and Conservation
Underwing moths are most common in deciduous forests and forest borders, and wherever their food trees grow. They typically rest on tree trunks during the day, which explains their forewings’ perfect tree-bark camouflage. They also often rest in caves, under ledges, on rocks, or among leaf litter on the ground. They are nocturnal (active at night) and are often attracted to lights.
Caterpillars feed in tree canopies at night. During the day, they either leave the food tree and hide among litter at the trunk base, or conceal themselves by pressing into crevices in the bark.
At least two species of underwings are Species of Conservation Concern in Missouri: the marbled underwing (C. marmorata) and precious underwing (C. pretiosa spp. texarkana); both are listed as vulnerable to extirpation from our state. The marbled underwing is rare to uncommon everywhere it’s found; its foodplants include willows and cottonwood. The overall range of the precious underwing is mostly east and south of Missouri.
The underwings (genus Catocala) used to be placed in the noctuid family (Noctuidae), alongside the owlet, dagger, miller, and dart moths, cutworms, armyworms, and more. But genetic research has shown they belong in the same family with tiger, lichen, and tussock moths, and a new family was created for this group: Erebidae.
The genus name is pronounced “kah-TAH-kuh-luh” and is from Greek words meaning “beautiful below” — a reference to the colorful hindwings.
If you want to see underwings during the day, it can be a challenge: Because of their camouflage, you probably won’t be able to detect them when they’re resting on bark. But you might disturb one as you draw near, and the moth will flutter away, flashing its bright hindwings . . . and so you follow. But just when you think you’ve closed in on the animal, it abruptly vanishes — having landed on another tree trunk, on the side away from you. Back to square one!
Because of their bright hindwings, underwing moths are favorites of amateur entomologists, photographers, and moth and butterfly collectors. They attract them at night using bright lights or use a sugar solution painted on the bark of trees as bait. During the warm summer months, a trail of baited trees and stumps skirting a Missouri woodland will attract many different species of this interesting group of moths.
What’s up with the species names? Many underwings have creative names like the betrothed, the dejected, charming, darling, connubial, inconsolable, tearful, sad, precious, serene, youthful, widow, oldwife, and so on. In the 1800s, when most of these species were first officially described in publications, scientists tapped into the imaginative, romantic culture of the time. One of these was Achille Guenée, a French entomologist who in the 1850s published Species des Nocturnes, a six-volume reference work on the world’s noctuid moths.
The caterpillars graze on vegetation, checking the growth of their food plants, and/or invigorating them by a form of natural pruning.
All stages provide food for predators. The bright hindwings serve to deter predators: Normally hidden beneath the drab forewings, their bright colors are suddenly exposed when the moth is disturbed, startling the predator and allowing the moth to escape. Also, a predator following the flashing colors of the moth’s underwings is often diverted from attacking when its prey seemingly disappears upon landing and again covers the bright hindwings.
In many cases, bright red, yellow, or orange colors combined in bold patterns with black usually signals “danger” to a potential predator. After a few tries at eating bees (which sting) or tiger moths or monarchs (which taste bad or are toxic), predators learn to avoid insects bearing the warning colors. But underwings apparently lack toxins; in this case, their coloration may take advantage of predators’ unwillingness to take a chance on another nasty-tasting meal.
Like other moths in the erebid family, underwing moths have tympana, hearing organs, which enables them to hear the sonar clicks produced by hunting bats. Being able to detect their archenemies’ presence helps them escape being eaten.