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