These wriggly balls are Western Tent Caterpillars. About every 7 years, they show up at population levels that threaten our trees. Tent Caterpillars only attack broadleaf trees and shrubs. If you see tents on conifers, it is probably the Silverspotted Tiger Moth which can also inflict severe damage.
These pests usually cause unsightly defoliation, but not to the extent of killing the tree. However, in years where the infestations are high, the damage can be severe enough to kill the tree, especially if it is under stress from other causes.
It is important to treat these tents as soon as possible due to the speed of defoliation. Be aware that the caterpillars do not stay in the tent, but migrate to other branches for feeding. You will miss many of the caterpillars if you choose to only remove the tents. Therefore, we treat the tent and several feet up and down the branch to assure elimination.
If you are noticing the “Big Bags of Cotton” on your trees please call us for advice or service at 360-629-7378.