Last Moths of the Year?

Possibly. Temperatures at night have gone below freezing four times since mid-September which has put an end to the songs of crickets and grasshoppers. Bees and butterflies are gone, either killed by the cold weather or hibernating. But in the last six days, I’ve seen a moth, Operophtera bruceata (Bruce Spanworm), flying in the woods. Operophtera bruceata is a brownish moth with faint markings and is in the Geometridae. On Thursday and Friday, I turned on my porch light and attracted about 25 moths each night. That’s the largest number of Operophtera bruceata I’ve ever seen at one time so this must be a boom year for them. Saturday and Sunday nights saw fewer moths and on Monday there were none.

Operophtera bruceata spends only a few weeks of its life as a moth. From late fall to May it is an egg hidden in cracks and crevices in tree bark waiting out the winter. In May and June, the larvae hatch and begin feeding. The larvae feed on a variety of common tree species but prefer aspen, sugar maple, beech, and willow. Pupation lasts until October.

Operophtera bruceata exhibits sexual dimorphism with winged males and wingless females. Apparently, this strategy works well as the moth is widespread in North America.

Other moths are also appearing at the lights. One is Lithophane grotei (Grote’s Pinion) which has only recently eclosed. It will not mate until next spring. Instead, Lithophane grotei will find shelter under bark or woody debris to hibernate and wait out the winter. A different life strategy from that of Operophtera bruceata. Its larvae feed on maple, birch, cherry, and apple leaves. Lithophane grotei is widespread in the northeastern US and Ontario and Quebec in Canada.

A third species at the lights was Sunira bicolorago (Bicolored Sallow). This species is common over most of the US and southern Canada east of the Mississippi River in moist forests. The larvae of Sunira bicolorago are generalist feeders of many herbaceous and woody plants and not just willows as its common name might suggest.

The fourth, and perhaps the final moth of the year, I saw was Xanthia tatago (Pink-barred Sallow). Like Sunira bicolorago, it occurs in moist forests where willows and cottonwoods grow as it is a food specialist and feeds exclusively on plants in the willow family (Salicaceae). Early larval stages feed on the catkins of willow (I can’t find any information about feeding on cottonwood catkins) and later on the leaves.

Weather forecasts over the next two weeks show decreasing day and night temperatures with highs rarely reaching the 50s and lows down in the 20s. Not unexpected weather for this time of the year. On sunny days some tiny moths or caterpillars might be out but evening mothing is probably over until March next year at the earliest. But that’s not set in stone as on December 15 last year there was this sighting of an Acleris sp. (possibly Acleris busckana). In the meantime, until temperatures are consistently at or below freezing, there will be other insects, spiders, and other small arthropods out and about waiting, I hope, to be photographed.

SOURCES CITED

Bug Guide:

Operophtera bruceata

Lithophane grotei

Sunira bicolorago

Xanthia tatago

Pacific Northwest Moths:

Sunira bicolorago

Xanthia tatago

Moth Photographers Group:

Operophtera bruceata

Lithophane grotei

Sunira bicolorago

Xanthia tatago