Could Ivel be afraid of the Red-Winged Northmoth? 

Fun fact about the Northmoth: it can overwinter by freezing solid and then continue on after it thaws - much like the Brimstone Butterfly on Earth. It's mildly surprising that they aren't all frozen solid at this very moment. 

Perhaps they arise at the behest of the Master of the Forest, who currently travels east with Ivel the Hunter and Cherisme his loyal companion. Oooo this story is going so well!

~N