Although a bit difficult to see in this photo, this caterpillar does have a unique cleft-shaped head, almost lending it a cat-like appearance. Part of the Geometridae family, Geometer caterpillars are frequently called “inchworms.” They only have two pairs of fleshy prolegs near the tip of their abdomen, along with the usual six legs on their thoraces. They move by bringing the rear part of their abdomens toward their thoraces, forming a loop out of their bodies. Many Geometers including this one, mimic twigs in posture and color. This species is Holarctic (coast-to-coast in North America and temperate Eurasia) and found in forests, woodlots, and parks. They are generalists and feed on a wide variety of trees and shrubs. This caterpillar will soon overwinter as a pupa in the soil or under leaf litter.      

This is thePeppered Moth, the subject of one of the most famous textbook examples of evolution in action. Haven’t heard of it? You’ll want to give it a quick Google to learn more!
Photo by Carolyn Taber on 10/8/20 in Missoula, MT.