Royal Alberta Museum: Invertebrate Zoology - Bug Facts

[Caterpillars and Other Immature Insects]

Fact Sheets: Commonly Observed and Asked About Insects and Spiders Found in Alberta

Columbia Silkmoth (Hyalophora columbia)

Columbia Silkmoth
Credit: Terry Thormin

Columbia Silkmoth - Caterpillar
Credit: Terry Thormin

INTRODUCTION

The Columbia Silkmoth is one of the largest moths in Alberta, reaching wingspans of 10 cm. The caterpillar can achieve lengths of 5 to 6 cm. Because the moth is active at night it is seldom seen. However, when seen it generates a lot of curiosity because of its size.

IDENTIFICATION

The size of both the moth and caterpillar eliminates almost all other species. The wings are reddish with a broad grey border, and there is a large tan spot thinly rimmed in black in both the front and hind wings. The front wings also have a black spot with a blue crescent in it near the apex of the wing. The green colour and rows of fleshy knobs separate the caterpillar from similar species.

DISTRIBUTION

The Columbia Silkmoth is found throughout central and southern Alberta in wooded areas. The subspecies in Alberta, H. c. gloveri, is often called Glover's Silkmoth, and is distributed from central Alberta and British Columbia south through the Rocky Mountain region to the mountains of northern Mexico. The eastern population, H. c. columbia is found from the maritime provinces and Maine west to southeastern Manitoba and northern Michigan.

TIME OF YEAR

Adults appear in June, with some individuals surviving into July. Caterpillars first appear by about mid-July and mature by early to mid-August. The cocoons are formed from leaves and silk, and are located in protected areas. They over-winter in this stage and the adults emerge the following June.

HABITAT AND HABITS

Caterpillars feed on a variety of plants, including rose, birch, maple, ash, oak and pine. For this reason they are found in wooded or shrubby areas. They sometimes appear in backyards if the appropriate plants are found. Because they have excellent camouflage, they are not often discovered unless their numbers are great enough to cause noticeable damage. Adults do not have mouthparts and do not feed. Females emerge from the cocoon with the eggs already preformed and are immediately ready to mate. They produce pheromones that attract the males. The males detect the pheromones with their feathery antennae, which are designed for that purpose. Adults are nocturnal (active at night) and are attracted to lights. For this reason they sometimes turn up on people's doorsteps.

SIMILAR SPECIES

The Polyphemus Moth (Antheraea polyphemus) is the only large moth commonly found in Alberta that is closely related. It averages larger, and is a lighter colour with clear eyespots in the centre of each wing. The caterpillar of the Polyphemus Moth is also green, but lacks the fleshy knobs, having instead clusters of bristle-like hairs.

COMMENTS

Most people who see this moth for the first time are amazed that such a large, attractive moth is native to Alberta. People are often amazed at the size of the caterpillar, but are also concerned that it might be doing serious damage to their trees and shrubs. This species is seldom found in numbers sufficient to be considered a pest species, and its beauty far outweighs its destructiveness.

For information on how to over-winter pupae of this species, see our fact sheet on How to over-winter butterfly and moth pupae

For more information on the Columbia Silk Moth you can visit the University of Alberta’s entomology collection species.

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Last update: December 10 2004