Winter moths

Morrison's Sallow, Eupsilia morrisoni

Toward the end of last Saturday's epic waterfowling excursion to Mosquito Creek Reservoir (that post, HERE), I headed off to check some meadows in the nearby Mosquito Creek Wildlife Area. The habitat looked prime for Short-eared Owls, and they're best found around dusk. In spite of waiting until nightfall, no short-eareds showed themselves, but we witnessed a phenomenon that made cruising around after dark worth the while.

While slowly threading the car along some sparsely traveled lanes, I noticed a moth flutter through the headlight beams. Then another, and another. In all, we must have seen two dozen. In warmer months no one would think twice about this, but the air temperature was 36 F! Brisk, to say the least. After seeing a few of these moths, and realizing that some sort of flight was occurring, I had to know what species was involved. Fortunately I had an insect net in the trunk - what self-respecting nerd doesn't carry an insect net? - and we put it to good use. Kristen Beck was also in the car, and with the next moth spotted, I hit the brakes, she leaped out net in hand, and Bingo! Mystery moth in hand.

It turned out to be a Morrison's Sallow, Eupsilia morrisoni, and the animal in the photo above is the very one that we captured. After puzzling over it a bit, I turned to BugGuide for expert confirmation and quickly got verification of its identity (thank you, "Novus philonatura!). With a name as a starting point, it was time to learn more about these curious cold weather moths.

Flipping to the section on sallows in Dave Wagner's amazing book, Caterpillars of Eastern North America, I learned the following: "This group includes many of our winter moths. All but the Red-winged Sallow emerge in the fall. The adults of several genera mate and lay eggs in the fall and early winter; others hibernate, periodically flying on warm nights, but wait until the first warm nights of late winter or early spring to engage in reproductive activities."

I then posted my photo to the Mothing Ohio Facebook page, and Kevin Bradbury weighed in, reporting that he sees this species coming to oozing maple sap about this time of year. Entomologist and moth authority Dave Horn then commented:

"Moths that overwinter as adults (like Morrison's Sallow) do so in a sheltered place such as under bark (or loose siding) where it might get quite warm in the afternoon of a winter's day. The high temperature in Columbus Saturday was 49 and the sun was out for part of that and I'd not be surprised if a hideout under south-facing bark reached 70 or warmer. If it gets that warm the moth can do the rest of the work by warming up, "shivering" the flight muscles to raise them to operating temperature (around 90-95 degrees). Then the moth can take flight, and as long as they keep the muscles moving they can maintain flight even at air temperatures below freezing. The "fuzz" on the thorax provides enough insulation so they can keep warm, so they need to find fuel (sap or syrup, or a moth-er's bait). (Yes, researchers worked this all out by installing micro-thermocouples into the thoraxes of moths and recording temperatures of fuzzy newly-emerged moths along with those of older, balder moths."

Very neat stuff, and I learned something new about the wide world of moths.