I get dozens of calls on GardenLine during the summer asking, “What’s that eerie, silky web covering the trunk of my tree?”
First, don’t panic: it's bark lice, a beneficial insect and not a threat to the tree in any way. And just as mysteriously as the web appeared on your tree, it will disappear within a couple of weeks.
The bark lice phenomenon occurs suddenly and frequently overnight. You walk out to get the morning paper and there it is. Just yesterday, that same tree looked perfectly normal.
The bark louse's favorite target is rough-barked hardwoods. The little critters are beneficial because they scour the bark for fungi, spores, pollen, lichen and other debris. While dining, they spin a web for protection. Once they are done with a tree, the web usually disintegrates within a week.
Bottom line: you don’t need to do anything. In fact, if you try to spray the web with an insecticide, it will bounce right off.