Polyphemus moth: One of our largest moths

Fluttering at the base of a bush caught my attention. I thought it was a butterfly but the antennae indicated it was a moth--a moth with a hairy body that resembled a tarantula. The moth was huge with a wingspan of nearly 5.5 inches. 

Male polyphemus moths have large, feathery, comb-like antennae to detect the female's pheromones

The polyphemus moth is unlikely to be confused with any other moth in the Pacific Northwest because of its size, tan color and translucent eyespots. I’ve never heard of the polyphemus moth before but I have heard of (but not seen) other giant silk moths--Luna and Cecropia (the largest moth in North America).

The polyphemus moth presumably was named after Polyphemus, a giant cyclops in Greek mythology, since the moth has large eyespots on its wings. 

Giant silk moths shouldn’t be confused with the silkworm moths that produce silk (Bombycidae family) for manufacture. Instead the name for giant silk moths (family Saturniidae) comes from the moths using fine silk to spin their cocoons. 

Polyphemus moths are the most widely distributed silk moths in North America, ranging from east coast to west coast and throughout southern Canada. Why haven’t I seen one before? 

When resting, polyphemus moths hang from a branch or twig with their wings folded above their back like a butterfly

The moths are mainly nocturnal and can be found near porch lights left on overnight. The one I found was on a bush next to the porch light. 

If it wasn’t windy, I wouldn’t have noticed the fluttering. Since the moths look like dead leaves or bark when their wings are folded, they can be hard to find. 

The adults don’t live for long either--one to two weeks. Without mouthparts, the moths rely on stored nutrients from their caterpillar stage to carry out their mission--to mate. 

Most of the moths emerge from their cocoons within one week of each other to ensure the males and females find each other. Their emergence is triggered by warm day and night temperatures which ranges from May to July in their northern range. 

They usually emerge during the day to allow their wings to inflate and dry before nighttime. Then at night the female releases pheromones (scents) that the male detects from far away with his elaborate antennae. 

Polyphemus moths are commonly found in wet forested areas, deciduous forests, orchards and wetlands at low to mid-elevations

After mating, the female finds suitable plants to lay three to five eggs on the undersides of leaves. She may lay more than 100 eggs but on different plants. The female lays the eggs on certain plants so the caterpillar doesn’t have to search for food. These plants include oak, maple, pine, birch, ash, aspen, elderberry, alder, sassafras, blueberry, grapes, willow, chokecherry, pin cherry, serviceberry and hawthorn. 

The eggs hatch within 10 to 14 days and the newly-hatched caterpillar eats its eggshell. Then the caterpillar begins an eating frenzy that allows its body weight to increase by a factor of more than 10,000. The caterpillars start out at three millimeters in length and increases to 70 to 100 millimeters.

By mid- to late August the bright green caterpillars reach full size. Since the caterpillars don’t want to lure in predators with marks left by feeding, they journey to a new plant to spin a cocoon. 

Polyphemus moths spin oval-shaped cocoons and incorporate some leaves from the plant. Once inside the cocoon, the caterpillar enters the pupa stage and changes into a moth. However, the pupa stays in diapause (a resting state) for the winter until the temperatures warm in the spring. The moth’s brief appearance provides us a chance to see one of our largest moths.