Nature Notes: A Maine Naturalist Afield
Transcript
Late autumn, a period marked by dwindling sunlight, frosty mornings, and a general browning of the landscape, is not a window of time strongly associated with butterflies. The foraging flights of the swallowtails and the skippers are long behind us. The monarchs have long ago made their exodus while the mourning cloaks have retired to their hidden chambers to pass the winter somewhere sheltered from the impending snow. Many a caterpillar that once patrolled the forest floor now lies immobile in hardened cases of chitin, buried beneath desiccated leaves that fueled their development in greener days.
Like most New Englanders, both wild and domesticated, I am busy preparing for winter days to come. Everyday, there’s firewood to stack, repairs to make, and food to cache away. The hibernal (or winter) solstice is still a few weeks out which means the amount of time I have to work on these autumntime chores is lessening by the day. Despite all this hurrying about from one task to the next, I do my best to keep an eye on the goings on in the surrounding landscape and, in doing so, have been surprised to find my assumptions about late autumn and butterflies weren’t entirely well founded.
True enough, there are far fewer butterflies these days than in the height of summer and early days of fall. During these portions of the year, the wood edges and meadows about our home are all aflutter with thousands of butterflies. Familiar with many dozens of species, many yet remain for me to observe and document personally. Now, after many successive frosts and nights below freezing, one might expect to find these same spaces barren, yet a handful of species persist.
One afternoon, while patching shingles on a rooftop, I stopped for a break and, crouched at the peak, surveyed the surrounding field. I spotted three yellow forms clumsily bounding over the landscape of low shorn grasses. They kept mostly to the wooded edge of the field, in the lee of the wind, and made regular flights to and fro. I surmised they were likely sulphurs by their flight, form, and hue. A few days later, while crossing this same section of field, I was passed by a small yellow butterfly. It was seemingly indecisive about whether or not to land and made many false attempts before settling on a dandelion whose flowering head was nestled deep within the grass. This individual was a Clouded Sulphur, one of Maine’s six species of sulphur butterflies, and one of the latest butterflies active in the state each year.
The sulphurs are so named for their often yellow-toned, sulfurous appearance. As caterpillars, uric acid is accumulated rather than excreted. Although typically a waste product, these acids are instead converted to pterins – the yellow pigments found in the scales of adults. Scales containing pterins contrast with UV reflective sections of the butterfly’s wings, therefore providing a more striking display for attracting potential mates (Rutowski et al. 2005).
The Clouded Sulphur is a widespread species within Maine, occupying a variety of open habitats and often in close proximity to us humans. Fields, lawns, and gardens are frequent haunts while the butterflies are active and each year, the state experiences three generations of emergence spanning from May to September (deMaynadier et al. 2023). Those butterflies I spotted roaming the field edges belong to the latter crop of emerging butterflies, a hardy group that has been documented in Maine as late as the 7th of December – the latest documented butterfly in the recently completed Maine Butterfly Atlas (deMaynadier et al. 2023).
Those adults still active come December will eventually meet their ends as nights lengthen, daily temperatures drop, and the first snows blanket the last remaining nectarous flowers. The species survives the coldest months as either larvae or pupae in a period of overwinter dormancy, known as hibernal diapause (Scott, 1981; deMaynadier et al. 2023). They pass the winter in a state of suspended animation, consuming nothing, respiring little, and very near freezing. Come spring, however, these overwintering individuals will issue forth across the state to initiate the multigenerational, season-spanning flight of Maine’s sulphurs.
As of late November, those remaining sulphurs are looking a bit worn and threadbare, but remain full of life all the same. Although the world, as they have known it, is rapidly changing, their season has not ended. On sunny days, they continue to patrol the field margins, a testament to their hardiness in a period of scarcity that few other butterflies could contend with.
Citations:
Clouded Sulphur — Colias philodice. Montana Field Guide. Montana Natural Heritage Program. https://FieldGuide.mt.gov/speciesDetail.aspx?elcode=IILEPA8010.
deMaynadier, P. G., J. Klymko, R.G. Butler, W.H. Wilson Jr., & J.V. Calhoun. (2023). Butterflies of Maine and the Canadian Maritime Provinces. Cornell University Press.
Rutowski, R.L & Macedonia, Joseph & Morehouse, Nathan & Taylor-Taft, L. (2005). Pterin pigments amplify iridescent ultraviolet signal in males of the orange sulphur butterfly, Colias eurytheme. Proceedings. Biological sciences / The Royal Society. 272. 2329-35. 10.1098/rspb.2005.3216.
Scott, J.A. (1981). Hibernal diapause of North American Papilionoidea and Hesperioidea. The Journal of Research on the Lepidoptera.