Plants & Animals

Plants & Animals

Underwing Moths

Hide, flash and fly is the survival strategy for one of Missouri’s most spectacular insects.

Underwing moths, with wingspans from 1 1/2 to 3 1/2 inches, are virtually invisible on tree trunks where they rest during daylight hours. Should a predator find one, the moth flashes brightly banded hindwings, startling the enemy. The predator’s split second of indecision allows the moth to fly away, alighting on another tree and disappearing once again. There are more than 60 species in the state, plus 40 varieties within those species.

Underwings are in the genus Catocala (Kuh-TOC-uh-la). The Greek name translates to kato for “below,” and kalos for “beautiful,” a perfect description of the moth’s colorful hindwings, normally concealed beneath the front wings. Besides tree trunks, the moths rest in caves, under ledges or among leaf litter on the ground. They only stir when darkness falls.

At night, underwing moths are vulnerable to attack by bats, but the moths have special organs on the thorax called tympana that allow them to detect a bat’s ultrasonic cries. Hearing an approaching bat, the moth takes evasive action. Underwings are strong flyers, and they might travel several miles in a night.

Adult moths find each other mostly by smell. Resting females give off a special scent called a pheromone that the male detects with his antennae. A pair mates tail-to-tail, with their wingtips overlapping.

Female moths lay eggs on the bark of the host tree, hidden in crevices away from the beaks of birds such as nuthatches and creepers. Incubating over the winter, the eggs hatch the following spring. The caterpillars quickly outgrow their exoskeletons (skins), and must molt (shed) several times as they age.

Underwings generally fall into one of two categories: those species that feed on oaks and/or hickories as caterpillars, and those that feed on willow or poplar. There are exceptions, such as the Magdalen underwing, Catocala illecta, which feeds on honey locust. Even as caterpillars they are nocturnal. As dawn approaches they press their bodies into crevices on twigs, branches or the trunk or travel down the tree to nestle in leaf litter. Young larvae slink along, clinging tightly to twigs. Older larvae walk, or “loop” like inchworms. They match perfectly the bark of twigs and branches where they rest motionless during the day. Some even have fringe-like growths on their sides that break up the outline of their bodies. A few species rest openly on leaves and, if discovered, thrash about violently, propelling themselves to safety or startling their attacker.

Eventually, the larva transforms into the next stage: the pupa. Underwing caterpillars do not spin cocoons but will lash together a few fallen leaves. The silk is spun from glands in the insect’s lower lip. Inside the pupal case, a dramatic internal reorganization of the insect takes place. About three or four weeks later, an adult moth emerges.

Seeking the elusive underwing moths, and their caterpillars, can be a rewarding experience for nature-lovers of all ages. The Conservation Department’s Butterflies and Moths of Missouri guidebook is a good starting point for learning more about Missouri’s moths. It is available for $18 plus shipping and handling, and sales tax (where applicable) by calling toll free 877-521-8632 or visiting www.mdcNatureShop.com or at conservation nature centers statewide.

Eric R. Eaton, photo by Donna Brunet