British Columbia South Coast
Found thousands and thousands of these caterpillars infesting a few Alder trees… they are everywhere! Haven’t seen any tents and the trees are now completely leafless. They are quite small, less than an inch in length. Have looked online to identify them, but no luck aside from the fact that I believe they are feeders! Any idea what kind they are?
We must begin with a compliment. Your request is so thorough and has allowed us to positively identify your insect in just a few minutes of web searching. You provided a location, a food plant and a photo. This is not a caterpillar. It is a Striped Alder Sawfly larva, Hemichroa crocea. The larvae are social feeders and BugGuide has an excellent image of a group feeding together.