Winter caterpillar

Large Yellow Underwing caterpillar. I took this photo on October 15th in Green-Wood and saved it for the first day of winter to illustrate the insect’s life cycle. I thought October was late in the year, but Noctua pronuba can be active even in the dead of winter, given a thaw. The mature caterpillars can live right through the cold months before turning into moths in May. This is not typical: Lepidoptera, the butterflies and moths, generally over-winter as eggs or nymphs (in cocoons). Pronuba is a species only recently, and accidently, introduced to North America. Starting in the Canadian Maritimes in the late 1970s, it has spread south and west rapidly and profusely.

Our winters are milder than they used to be. (And by “used to be,” I mean as little as half a century ago; and by “little as,” I mean I’m nearly of half century vintage myself.) This means that more and more insects are surviving a season that once cut their numbers back severely. One example: the forests of the intermountain West are under severe attack from Western Spruce Budworm and Douglas Fur Tussock Moth, native defoliating species that have been supercharged by both fire suppression strategies and warmer weather.