A few weeks ago, I discovered a large, bright green caterpillar in the yard. It was the size of my thumb with small dark spots and several hairy spines on its back. The caterpillar was inching through recently mowed grass and I tried to entice it onto a stick to get a closer look. It held fast to the blades of grass, so I went indoors to check my guide to butterflies and moths and discovered it to be the caterpillar of the luna moth (Actias luna).

I have not seen these beautiful moths in their caterpillar stage before, so I returned to where I had left it in hopes of snapping a few pictures with my camera. It may be large and fat, but it sure moves fast – it was nowhere to be found.

Since my encounter with that green caterpillar, I did some reading on these special summer visitors. The luna moth is one of our more recognizable moths due to its larger size and beautiful pale green color with long tail and two moon-like spots that give it the “luna” name. They are found from Nova Scotia west to Saskatchewan and eastern North Dakota; south to central Florida, the Gulf Coast states and to eastern Texas.

In New England, the caterpillars prefer to feed on the leaves of white birch and hickory trees. In southern locations they also feed on sweet gum, persimmon, sumac and walnut trees. The one I found was located a few feet from two black walnut trees my father had planted back in the early 1970s.

The most distinguishing feature of the luna moth is its large size, placing it in the megafauna category of the moth world. The adult wingspan is between 3 and 4 inches long, making it one of the largest moths found in New England.

In our region, the adult luna moth emerges from its cocoon in May or early June and lives for only one week with the single goal of breeding and laying eggs. It doesn’t even eat during its one week as an adult. Mating takes place after midnight, and the female will lay up to 400 small eggs on the underside of leaves (usually a tree that is the preferred food source of the caterpillar) within hours.

The eggs hatch within two weeks and the larva (caterpillar) will feed for about eight weeks before it spins a silk web and wraps itself in a leaf to pupate and begin its metamorphosis into adulthood. It will remain a pupa for nine months before emerging to repeat the cycle. In its northern range it has one breeding cycle per year and in its warmer southern range it can have two or even three cycles per year. There is some variation in the luna moth’s appearance based on its geography and the time of year of the brood. The southern adults have pink edges to their wings for the early brood. Here, the wing edges are yellow.

The luna moth is not a common sight, partly because of its short adult lifespan and its nocturnal nature. However, it is also a moth species considered in decline by some. The last time I saw a luna moth it was attached to my window, wistfully peering into the house like a surprise guest from another world. If you see one, remember it will only be alive for a single week. Enjoy it, take a photo if you can, but please don’t disturb it from the important task of reproduction. Its life may be fleeting but what a beautiful week it is, and how lucky we are when we encounter one of our most magnificent creatures.

We live in a beautiful place called The Last Green Valley National Heritage Corridor full of amazing and fascinating creatures. I hope you’ll join me and others as we work to care for, enjoy and pass on this special place we call home.

Bill Reid is chief ranger of The Last Green Valley National Heritage Corridor and has lived in the region for more than 35 years. He can be reached at bill@tlgv.org.