Out in the Cold

It’s early morning. Still dark. Outside temperature is about 0° C and there are several Bruce spanworm moths on the window. The other evening, only a few degrees above freezing, we counted nearly 6 dozen on that same window, all drawn to the kitchen light.

As I discovered, these moths are unusual in several ways — not the least of which is their ability to remain active in cold weather.

Greg Pohl, Insect/Disease Identification Officer with Natural Resources Canada, explained how this is possible:

“Winter moths are quite remarkable. They’re adapted to fly at temperatures as cold as -3°C. They put quite a bit of their energy reserves into antifreezing chemicals in the bodies, and they also “shiver” to warm up their bodies and flight muscles to the point that they can fly. So even though they’re “cold blooded”, they have some ability to warm their bodies. They’re very highly adapted to fly late in the fall, and thus avoid many predators. But those survival skills wouldn’t likely be developed in warm-weather day-flying species like monarchs.”

Male Bruce spanworm moth

If not for finding these nondescript moths in such cold temperatures I might have paid them little heed. Lesson learned: sometimes the plainest wrapping holds the biggest surprise.

Bruce spanworm   Operophtera bruceata

What Are They Thinking?

We’ve had cold nights, cool days, ice on the windshield and the deck, several small snowfalls and now this: a large hatch of moths.

What the heck is going on? This ain’t the right season to be flying around.

Or is it?

The moths gather by the dozen at night on our uncurtained windows. During the day they flutter and flop around the yard, along the gravel road and in the sunbeams in the woods. Getting clear photos of them has been a challenge as they never really stop for more than a moment. They’re in a hurry.

Bruce spanworm moth

Turns out they’re doing exactly what they should be doing at this time of year. They’re Bruce spanworms and they’re “late season” moths. No kidding. Seems the drop in temperature is what kicks off the mating season.

Another quirky characteristic — all the ones with wings are males. Females are wingless. This frenzy has been going on for a couple of weeks. There’s no time to eat, only to mate and lay eggs that will hatch next spring.

Get busy guys.

Bruce spanworm moth

Bruce spanworm   Operophtera bruceata