A Gentle Giant - the secret life of the Columbia silkmoth

Through the dappled light of the boreal forest, the soft reddish-brown wings of a Columbia silkmoth beat gently as they fly away from my hands. Although newly emerged into this large, fuzzy creature, there is no time to lose in finding a mate. Like other silkmoths, they are destined to live only 1 to 2 weeks in this spectacular form.

These gentle giants have 3 1/8 - 3 15/16 inch (8 - 10 cm) wingspans and soft brown to reddish-brown wings. The tips of their wings are rounded and a black and white line separates the inner reddish-brown coloration from the thick gray-white band that encircles the outer edges of the wings. A white crescent-moon-shaped spot is found in both the forewings and the hindwings and a large black spot can be seen on the apex of the forewings. They are commonly mistaken for their close relative, the cecropia moth, but are smaller and lack the reddish coloration in the middle stripe seen in cecropias.

Columbia silkmoths (Hyalophora columbia) are a member of the family Saturniidae, a group of giant moths with gorgeous wings and short lives. Adult Saturniidae species lack functioning mouthparts and live without ever tasting the sweet nectar of flowering plants or even drinking water.

Emerging from their silvery-brown cocoons from May to June, Columbia silkmoths quickly set to work looking for mates. Both males and females have large feathery antennae and males, with the largest antennae of the two sexes, use theirs to track the pheromones produced by females.

After mating females lay 1 to 2 eggs at the base of tamarack needles in the eastern United States and Canada where tamaracks, also called larch, (Larix laricina) are the host species for the moth. In the western United States females lay their eggs on a variety of host plants including western chokecherry (Prunus demissa), bitter cherry (Prunus emarginata), bitterbrush (Purshia tridentata), wild roses (Rosa spp.), willows (Salix spp.), buffalo berry (Shepherdia argentea), Russian olive (Eleagnus angustifolius), and buckbrush (Ceanothus spp.). Within two weeks, caterpillars hatch and begin to fatten up on the bounty of their host species. By September, mature green caterpillars are ready to form their cocoons.

These caterpillars build their cocoons close to the ground on their host plant. In these hairy enclosures, the moths overwinter, finally emerging in May through June to start the cycle over again.

When I worked at the Paul Smith’s College VIC I had the honor of releasing some of these beauties into the forest where we hoped they might stay to rear the next generation of silkmoths in our tamarack-covered bog. Although they are not listed as a threatened species, they are extremely rare to see. In the Adirondacks, there have been only 2 reported sightings on the BugGuide data list and there are only 7 observations reported to INaturalist between 2014 and 2021. Their global conservation status according to NatureServe is currently G4, apparently secure, although rare to see and suspected of decline.

If you’re in the mood for a treasure hunt, here are some helpful tips for finding Columbia silkmoths in the Adirondacks:

Like all silkmoths, Columbia silkmoths are nocturnal, so make sure to use an appropriate light source away from street lights and other distracting light sources. (You can learn more about choosing a light source over at Project Silkmoth)
Look for Columbia silkmoths near their host plants (tamaracks/larches) and in areas with boggy, acidic soils where tamaracks are likely to grow.
Know what stage to look for. Look for adults between May and June, caterpillars between June and September, and cocoons tucked in the lower trunk or branches in the winter.
Observe responsibly. As always, make sure you are following the rules and regulations of the park or forest you are in and avoid harming moths, caterpillars, their host plants, or their cocoons.
If you are lucky enough to see one, report it. You can help us better understand this species and its status by reporting sightings to Project Silkmoth and citizen science platforms like INaturalist.