The name 'tree cattle' refers to the way these insects form 'herds' on tree trunks. The striped ones are the nymphs (juveniles). They feed on dead bark, lichens, fungi, and are entirely harmless to people, trees, plants... though people sometimes worry that their trees are being attacked when they see aggregations of these insects, but that is not so. The adults measure 6 to 8mm in length.