The fourth Thursday of November is upon us, and this can mean only one thing – winter moths are coming! A few days ago, while trying to decide if this year we should have a turkey or two turkeys for dinner, Kristin looked up from the menu list she was working on and said, “Thanksgiving moths should be here soon.” I never realized it, but this is a much more appropriate name for these insects, members of the family Geometridae, which begin to flutter around the lights of our house around this time of year. Sure enough, that very night the first Winter moth (Operophtera brumata) came to the light of the kitchen window, and their numbers have been picking up since.
Winter moths are interesting animals. Unlike most species of moths and butterflies, they are strongly sexually dimorphic. In fact, while the male looks like your typical, grayish-brown geometrid moth, you will be hard pressed to recognize the female as a member of the same order of insects. She is plump and flightless, with wings reduced to tiny lobes that often resemble tufts of hair. Her mouthparts are reduced (not much to feed on for a moth at the end of November), and the only clue that she is in fact a moth comes from the scales that cover her entire body.
In the coming days we will be seeing more and more mating pairs, until the arrival of permanent freezing weather kills them all off. But their eggs, safely hidden in the bark of maples that grow around our house, will hatch next spring, and thousands upon thousands of small, green caterpillars will commence their prodigious pooping on our deck at the end of April. Some years there are so many of them that the foliage of our maples is almost completely gone by the end of May. The incredible abundance of this moth is a clue to the fact that this species does not really belong here. It is an invasive species that arrived from Europe in the 1930’s, and has since spread across the entire North American continent. And because it does not have too many natural enemies here, it is able to breed in numbers higher than those of many native moths. A closely related, native species, O. bruceata, is rarely seen in similarly high densities.
Winter moths (Operophtera) are not the only moths that come out around this time, and also not the only ones with remarkable morphological differences between males and females. I found another geometrid moth, the Fall Cankerworm Moth (Alsophila pometaria), yesterday on a tree trunk in Estabrook Woods. These animals are even stranger, with females completely devoid of any traces of wings, and resembling a velvet sausage running on long spindly legs.
Although winter moths are not the only insects active at this time of year, and some insects remain active even during freezing weather, their appearance reminds me of two things. First, that the insect season is truly over, and they are the last things to come to the lights of our house until spring. And second, that this Thursday night I will assume the appearance of a winter moth female, stuffed to the breaking point like a sausage, and definitely incapable of flying.