There’s a long-held myth that cats wag their tails when they’re angry, and dogs when they’re happy. But this isn’t always true. Dogs’ tails have a number of different purposes, including aiding balance, fending off insects, and increasing or minimising scent. And just as humans use body language to communicate emotion, so do dogs. The wag of a dog’s tail can communicate a great deal about how a dog is feeling, both to other dogs and to humans.
You can tell a lot about a dog’s mood by how fast his or her tail is moving and the direction of the wag. Studies show that dogs wag their tails to the right when they are happy and to the left when they are frightened. While the points below provide a rough guide, when reading a dog’s tail, it is important to look at their entire body. If a dog’s tail is wagging to the right but he or she has stiffened muscles, dilated pupils, tense facial muscles, or ears pinned forward or back, it is probably best to keep your distance.
A tail held high in the air, whether wagging or still is a sign of assertiveness – a message to other dogs to back down. "Alpha" or dominant dogs carry their tails higher to release more of their scent.
This is a dog’s way of flying under the radar. A tail held low signifies fear or caution. Your dog may be feeling a little frightened or anxious about their situation.
The common saying “walking with a tail between their legs” comes from the common dog behaviour. When dogs are frightened or insecure and don’t want to release their scent, they will tend to walk with their tail between their legs. A slow wag with tail at 'half-mast' in neither a particularly dominant (high) nor a submissive (low) position is also a sign of insecurity.
A slight wag is usually seen during greetings as a tentative "Hello there," or a hopeful "I'm here!" A broad wag is also friendly and is the dog’s way of communicating that he or she is not challenging or threatening you. This kind of wag is probably the closest concept to the happiness wag, especially if the tail seems to drag the hips with it.
A tiny high-speed wag (almost like a vibration) can be a sign that a dog is getting ready for action – often a run or a fight. Be aware that if your dog’s tail is held high while wagging quickly, it could be an active threat.
Some breeds of dogs, like whippets, are more likely to hold their tails low, whereas Akitas and Pomeranians have naturally high tails. To more accurately understand your own dog, ask your vet for more information.