I have had a few worried customers bring me jars full of these little striped bugs. They are called Barklice and they are harmless to both you and your plants. There is no need to spray them. Barklice eat lichen and decaying plant material. When they hatch out there can be hundreds of them swarming around on things. You may also notice a fine white webbing on the trunks of the trees that looks like a white stocking has been pulled over them. This is their protective house. They won't hurt anything and will go away on their own.