Second, these caterpillars were present at incredibly high densities:
I identified them as Fall Cankerworm (Alsophila pometaria), a common native moth that often causes severe defoliation. Jumping forward five or six months, I've been noticing moths flying around everywhere recently, even in the middle of the day.
These are the male Fall Cankerworm. The really interesting thing is the female: she is completely lacking wings, and must crawl up a tree (or in this case a house) to lay her eggs!
female laying eggs
Now, to link this back to my last couple of posts, I have been seeing many species of birds eating these moths (or perhaps also other species, as there a few moths that emerge at this time). For lingering insectivores, this is one of the only sources of food right now, and they have been taking advantage, like this Bay-breasted Warbler from Mississauga on November 19. Once things get cold enough to kill the moths or force them into hiding, I expect the birds to start getting desperate and increasingly showing up at those places with other sources of food.