May/June 2006For Wildlife Watchers: Luna Moth by Rob Simbeck, photography by Phillip Jones
Most animals, like most people, aren't fated to win beauty pageants. The world is teeming with creatures that don't hold up well under aesthetically driven scrutiny. Among insects, for instance, it's not easy to find empirical support for Keats' dictum that truth is beauty and vice versa. Truth with a magnifying glass fares even worse. There are nearly a million species of beetles, clearly making them a triumph of survival and adaptation, but you will not find them adorning greeting cards.
Butterflies are, of course, the big exception. Light, ephemeral, dazzlingly colored, they capture our minds and emotions, helping to give insects what little cachet they have. With moths, on the other hand, we are often flapping back into the realm of the average, the pale, the ordinary.
That's why the luna moth is such a lovely surprise. Coming across one is like finding a twenty in a pocket on laundry day.
"Their long tails," says Rita Venable, former editor of Butterfly Gardener for the North American Butterfly Association, "trail and toss behind their green-like-no-other wings, mesmerizing us with their aerial instability. You can't help but stop and watch one when you see it."
Luna moth - Actias luna
Description: 5 to 6 inches long, 3- to 4-inch wingspan. White body, pinkish legs, lime green wings with eyespots, feathery antennae.
Habitat and Range: Deciduous hardwood forests along the East Coast from Canada to Florida. Throughout South Carolina.
Reproduction: During 1- to 2-week adult phase. Eggs laid on host plants. Five larval stages and a pupal stage.
Viewing Tips: Brief breeding periods, especially in spring, offer the most predictable opportunities. Rural areas, particularly near woods with water.
They hold many attractions. They are, first of all, large, up to six inches in length with a wingspan that can exceed four inches. They are strikingly beautiful, a vibrant lime green, sometimes with maroon or yellow highlights at the edges, and transparent eyespots on each of four wings. And they are rarely seen - they are nocturnal, and few of us spot them, fairylike, passing their genes to the next generation. A brief adulthood is the insect's last gasp, a narrow window of time in which it is scripted to reproduce quickly and get off the stage. Its doom is certain: the adult luna moth has not even been granted a mouth by evolution, so it lives off fat ingested in the last days of its caterpillar stage, mates, and dies in a matter of days.
The luna moth is named for Luna, Roman goddess of the moon. It is a member of the giant silkworm family, one not related to the Oriental silk-producing moths. It prefers deciduous hardwood forests and occurs from Canada to Florida along the East Coast. The trees it prefers vary from birch in the North to hickory, walnut and sweet gum in the South. Latitude also affects the number of broods, which generally varies from one in the north to three along the Gulf Coast.
"It is not an uncommon species in South Carolina," says Billy McCord, a wildlife biologist with the Marine Resources Division of the S.C. Department of Natural Resources. "There are enough rural areas and swamp forests with plenty of sweet gums along river bluffs that the species is still doing well."
Procreation takes place during that very brief adult phase, which begins with a mid-morning emergence from the cocoon. The female is already full of eggs, holding from 150 to 250, and several hours after nightfall she emits a pheromone from a gland at the back of her abdomen. Males, who can sense the pheromone from a great distance with feathery antennae, find the females and the two mate, remaining joined for hours. The female begins laying eggs, a few at a time, on the undersides of food plant leaves. The effort burns the fat she has stored, and she is dead not long after laying her eggs. The male is more than likely able to fertilize several females, but he will not live long either.
In South Carolina, the year's first brood - over-wintering cocoons - emerge as adults in late March or early April. Weather conditions, particularly rainfall, help determine the timing of the second brood, which can vary from late May through early July. A third brood can emerge from August 1 to mid-September, and even a partial fourth is possible.
The eggs hatch in about ten days into caterpillars that are eating machines. They grow through five larval stages, spending about a week in each, with the fifth lasting a little longer, their skin splitting each time as they grow. The caterpillar is thick and green with a brown head, a yellow stripe down each side and rows of red tubercles. It gets to be three-and-a-half inches long before entering the pupal stage, spinning silk from near its mouth and wrapping itself in a light cocoon, often with a leaf as an additional wrap. In many cases it drops to the ground before doing so, wrapping itself with whatever is available and becoming virtually impossible to spot amid the leaf litter.
Normally, it is in the pupal state for two to three weeks, except for those that overwinter. Emergence begins with the secretion of a liquid that helps soften the cocoon, which the moth scrapes and tears with small spikes at the end of its forewings. It squeezes through a small hole and crawls onto a tree trunk or branch.
There are conflicting reports on the health of luna moth populations, with human development often determining local viability.
"I don't think there's any doubt that localized populations have suffered greatly from urban sprawl, increased numbers of electric lights, pesticide use and loss of larval food plants," says McCord, "but over the broad scope of things, the South Carolina population is probably still in pretty good condition, especially along the coastal plain." Natural predators include spiders, toads, bats and birds, including owls.
For the time being, if we're knowledgeable and lucky, we can help preserve suitable habitat for luna moths and give ourselves continued opportunity to cross paths with one of nature's loveliest creatures.