By now you've probably noticed the dozens of small, fairly drab moths clinging to buildings around town in the morning. A little bit of internet searching has me thinking that they're probably Bruce Spanworm (Operophtera bruceata) moths, and believe it or not it's normal for them to be showing up this time of year.
All of the flying Bruce Spanworm moths you see are males, as the females lack developed wings. In October (through to early November, depending on the weather), the males seek out the flightless females which then lay eggs in places like bark crevasses. These eggs overwinter and hatch out in the spring.
The larvae (known as spanworms or inchworms), like all caterpillars, can do some damage to tree leaves but usually don't cause permanent harm to the trees themselves.
As always, click on the photo for a larger version.