Soltice “” the invisible annual pivot point


This winter solstice, the official start of winter, was emphatically punctuated by a total eclipse of the moon early Tuesday morning (the actual solstice occurred Tuesday evening).

When this column was filed Monday morning, the prospect of good viewing conditions for the eclipse looked grim. But whether you could see it or not, there is something wonderful about the earth acting as a gigantic lens, refracting a dim echo of sunlight through its atmosphere and onto the shadowed moon, to mark the shortest day.

Some similar celestial drama should signal each solstice. The moment of the lowest sun is predictable — cultures have noted and celebrated it for millennia — but it’s nearly invisible, an undistinguished moment on an undistinguished wintery day. And yet the solstice echoes throughout the natural world. A colorful alignment of celestial bodies seems like a fitting marker for this turning point, which truly is a critical point on the Wild Side.

On the surface, the landscape looks bleak during the first few weeks of December. The trees are bare, the growing season ended weeks ago, and most migratory species are in their winter quarters. But a careful observer can find a surprising amount of wildlife still active during those weeks; hints of the past summer persist, and there are even species that time their reproductive lives to those weeks leading to the solstice.

Most obviously, Islanders may have noticed swarms of grayish moths around porch lights and windows on warm evenings earlier this month. Aptly named, these winter moths emerge and mate in weather that would immobilize or kill most insects. As you’d imagine, they have evolved unique proteins and enzymes that function well in cool conditions, allowing energy to flow and muscles to contract. The winged males flutter in search of the scent of wingless females, which have climbed onto the bark of the trees that will feed their caterpillars at leaf-out next spring.

While activity in cold weather is not a common pattern among insects, the winter moth is hardly alone. There are also winter crane flies and lacewings that turn up at porch lights in December, similarly adapted to enduring cold, mating, and laying at this unpromising season. The approach seems incongruous for cold-blooded animals, but it has advantages: most potential predators are either inactive or far to the south, and these cold-adapted species enjoy a window of relative safety at a critical point in their life cycles.

December also features the tail end of the summer season for many species. A few grasshoppers persist in sheltered spots, and on a mild days a few butterflies can still be found (over the years, a half-dozen species have been recorded here in early December). On a warm Saturday earlier this month, I found five distinct species of flies still active at Cedar Tree Neck, warmed by the sun on the open beach, along trails, or as they swarmed over ponds. Straggling warblers linger in our region in small numbers, even as our winter resident birds continue to arrive and settle in. And I’ve been told that a few striped bass dally in our waters into December, making leisurely headway toward the Chesapeake.

But by the time of the solstice, the game is over. Summer insects that hadn’t gotten around to dying have done so. Those few insects optimized for late autumn, like the winter moth, have run their course and encountered conditions lethal even to them. Migratory birds that are truly migrating have gotten the message and left, and any colleagues they leave behind are likely doomed by whatever afflicts them: Injury, sickness, or just an unfortunately dim migratory impulse.

And then, at the moment it ends, the annual cycle starts again. The point of the solstice, of course, is that it’s the shortest day. The following day is longer, if only by seconds, and the lengthening accelerates as we approach the March equinox. Just as summer did six months ago, winter begins to wane at the moment it begins. And within a few short weeks, Island wildlife will begin to respond to the lengthening days and higher sun. Silent around the solstice, a few resident birds like chickadees and house finches will be singing again by mid-January. The average temperature lags behind day length — the coldest day, on average, comes around January 20 — but the push toward spring has already begun.

The length of the day exerts enormous control over nature. It’s a pervasive, unfailing signal of the turn of the seasons, prompting plants and animals both simple and complex to alter their hormones, their behavior, and their activity level.

I understand the physiology of it all, and I know exactly what will happen. But still, every year, the solstice catches me off guard, surprising me with how dramatically the natural world can pivot on an invisible point of time.