There are many insects that attack trees and shrubs year-round.  Among the worst are most certainly Bagworms.  Bagworms can completely devastate a tree or shrub, literally, in days.  Sometimes insect damage is noticable right away and at other times it takes a while for a homeowner to notice.  It is very important to address any type of insect or disease damage right away.  Perhaps the most important reason is that unhealthy plants put out a pheromone-like substance that screams, "Hey, I'm sick, my defenses are weakened and I'm ripe for an infestation of insects or disease."  Bad news for the host plant as is evidenced by the photos.