from Kris Bayas, Volunteer Coordinator, WSU Extension-San Juan County
We have received several calls about webbing in trees. This is fall webworm, and you can tell the difference between the fall webworm and the tent caterpillar by the way the fall webworm encloses itself in the nest.
Since these caterpillars are feeding on foliage that is just going to drop off soon anyway, we seldom recommend anything other than pruning off infested branches or physically removing the webs/nests.
For information, see the WSU HortSense entry.
Fall webworm can also be an orchard pest. There is a great page on the subject at WSU’s Tree Fruit Research & Extension Center.
Photos Credits: Webworm photo from Wikimedia Commons;
Nest photo from gardeningknowhow.com.