Hyphantria cunea

The adult moth appears to have no generally used common name, but the caterpillar is the Fall Webworm. It is usually not devastatingly abundant on southern Vancouver Island, but where it occurs the caterpillars are to be seen in their hundreds in huge, spreading webs draped over the alder branches in late summer. Pupation takes place in the fall in a cocoon, and emergence is in the following spring. The adult moths vary in appearance across the country, but the ones I have seen here are pure white with no markings on the forewings at all. They are smaller than Spilosoma virginica, which usually has one or two small black spots on the wing.