Luna Moth caterpillar life cycle green giant beautiful | The Old Farmer's Almanac

Cinderella in Silk

Luna Moth at Window
Photo Credit
Henry Walters
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Midnight. A whomp against the window: a glimpse of wings. Big wings.

Birds leave feather-traces in oil on the glass, but this visitor leaves almost nothing—a couple fingertips of dust on the outside sill. It looks like dust, but under a lens the particles show themselves as beautiful, variegated scales, like a dense bouquet of colored-pencil shavings, or the foamy ruffles of an old-fashioned ball gown. And this from an insect who has just seven days to wear this elaborate dress.

Scales from the Eyespot of an Adult Luna Moth
Photograph by Peter Znamenskiy

At my window is an adult Luna Moth, one of the most striking members of the family Saturniidae and of the sub-group commonly known as the Giant Silk Moths. Not to be confused with the domesticated silkmoth (Bombyx mori), these are some of North America’s largest moths, one of which (the Cecropia) has a wingspan of up to five inches. Many species are uncommon or declining over large parts of their range, and the appearance—or apparition, really—of one at your window, no matter the hour, should rouse you from slumber.

Adult Luna Moth
Photograph by Henry Walters

The Luna is pressed to the glass like a lizard, soaking up the light. Its green wings taper into two curling streamers that dangle down behind, excessive as a pianist’s tailcoat. Its wide antennae spread out like the fronds of a tiny yellow fern—this is a male. All this elaborate get-up, the animal’s “adult” stage, lasts less than a week. It takes neither food nor water: its one aim is to find a mate in the short time remaining to it. Eggs are laid and hatched in late spring; the caterpillars eat nonstop all summer; and by early fall they have cocooned themselves inside a durable silk shell, in which they bide the entire winter, to emerge as moths in spring.

Polyphemus Moth Larva
Photograph by Henry Walters

Pending permission of the other members of the household, one can raise many species of these silk moths in one’s very own home. Given proper care over the course of a year, the insects will go through each stage of their preposterous life-cycle, right before one’s eyes. Forty-two caterpillars of the Polyphemus Moth, close cousin to the Luna, currently hang from sprigs of red oak in my living room—hairy, fleshy, unglorious things. Roughly the slime-green color of Ghostbusters’ “Ectoplasm,” they grow to be nearly four inches long and thicker than an index finger. The sound of their chewing is audible at all hours: in case you never read Eric Carle’s timeless children’s book, these caterpillars are very hungry. While they rarely cause any lasting damage to trees, I myself have had to forage whole branches to bring back to my voracious charges. Once in a while, venturing out to the woods, my headlamp beam combing for red oak, I could mistake myself for some strange creature of the night, drawn on by the light.

Adult Polyphemus Moth
Photograph by Henry Walters

We are expert at finding likenesses. I am like this. This is like that. One thing transforms into another, and the whole world is held together by the continuity. But it’s the unlikeness of these animals—the dissimilarity between amorphous caterpillar and the alien, marvelous, winged thing that emerges from its winter cocoon—that holds me, that makes me rub the sleep out of my eyes, not quite believing in this fragile green form on the glass.

Luna Moth at Window
Photograph by Henry Walters

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