As you can see, unlike many caterpillars that venture out on their own to feed, these guys like company and spend a large part of their caterpillar life with a bunch of friends in a silken tent. Western Tent Caterpillars can be found from southwestern Canada and the western US to northern Mexico. On years where their population is high, the caterpillars can completely defoliate their host tree. When the caterpillars reach their later stages of development, they will break up the group, heading off individually to continue feeding and eventually pupate. In Montana, the adult moths are usually found from mid to late summer.
And an interesting aside that we came across…according to the University of Montana Bird Ecology Lab’s Instagram account, “Young caterpillars hang together and create these silken tents which they for both protection and molting. But these tents are useful for more than just caterpillars – Lazuli Buntings will also use the silk to hold their nests in place! Female Lazuli Buntings have been observed making multiple trips to harvest the silk from these tents. They’ll then line the inside of their nests with a bit softer material like fine grasses and animal hairs.”
Size: Mature larvae are about 2 inches (4.5-5.1 cm) long
Photo by: Karen Weaver on 4/24/22 near Darby, MT