It's the time of year when you might see this in a branch or two in trees. These are tent worms and they are not very destructive. They will defoliate a limb but aren't going to kill the tree. When we see this and the branch is in reach, I will cut it off. However, in my opinion, it doesn't warrant an insecticide treatment. A lot of people (including me initially) mistake these for the Gypsy Moth Caterpillars. If you ever lived in an area that was devastated by the Gypsy Moth, you will probably understand the reason for concern. There are many areas in the US that where forests were destroyed by this insect. Fortunately, while the 'tents' look the same, these guys are not destructive and it's best to leave them be.