An invasion has been going on unnoticed across a portion of the state this summer and early fall. It all started back in mid-July, when I had several inch-long moths show up at my back deck lights. I captured a few and set them aside to examine under the microscope but hadn’t thought much of it at the time. Later, as I was preparing the specimens, I noticed a distinct copper color of the hind wings. Over the next week, several more of these moths mysteriously appeared in the house. . .
Within days other reports started popping up elsewhere in the state. By the time October rolled around, I had reports of “home invasions” from over a dozen counties in the southern and western portion of Wisconsin. The common feature in these cases was the metallic copper color of the hind wings, indicating the Copper Underwing (Amphipyra pyramidoides). The species is fairly widespread, but isn’t usually encountered in large numbers. In most cases (mine included) it was only a handful of these moths that snuck indoors. However, in a few situations, the moths were congregating by the hundreds (or even thousands) on homes or garages and were being quite a nuisance. David Wagner does mention this phenomenon in the Owlet Caterpillars of Eastern North America.
I’m not exactly sure what caused the boom of activity this year, but the caterpillars (commonly called “humped green fruitworms”) must have had perfect conditions to develop earlier in the year. Luckily, with fall and the cooler weather the invasion seems to have stopped. Who knows what next year will bring?