Why Dog Wag Their Tail? – Dogs are highly social animals with ancestral roots in the pack organization of wolves. Because they live in social groups (which, for pet dogs, is comprised of their human family) they have developed a complex language using facial expressions, body postures and tail movements.
Dogs communicate to other dogs and to people using both physical and vocal cues. Among these signals, tail movement is quite expressive. A loosely wagging tail communicates friendliness and some excitement; one held low can also be indicating fear or anxiety. Although most tail-wagging dogs have good intentions (letting the “recipient” know of their friendliness), aggressive dogs may also wag their tails. Threatening or aggressive dogs will wag their tails more rapidly at the tip and hold their tails high.
What about dogs who have no tails, either naturally or through docking (such as Old English sheepdogs and Australian shepherds)? Next time one greets you, notice how the dog compensates with other body language to tell you he’s friendly.