A dog's dew claws are located on the inside of the legs, higher than the other claws, and rarely touch the ground. Some dogs occasionally have rear dew claws, and these have less muscle structure than the front dew claws. While most dogs don't seem to have much use for their dew claws, others use them for various activities.
Since the dog's dew claws are located higher than the other claws, people often assume they have no use. Actually, a dog may use his dew claw to hold on to objects, such as bones, to keep them steady as they are chewing on them. They might use a dew claw to scratch an itch or remove something from their teeth. Some of the faster, slender-legged dogs extend their legs and push off on the dewclaw to give them more speed.
Dew claws can get snagged on things like blankets and carpeting, possibly causing trauma for the dog. If a dew claw becomes snagged, the dog may pull hard in a desperate attempt to free himself. This could tear the dew claw off the paw, causing an injury that needs professional medical attention. If the dew claws are not kept clipped, they can curl inwards, creating a greater chance of injury.
The dew claws need to be trimmed more often than the other nails because they do not touch the ground when the dog walks. The other nails naturally wear down slightly as the dog walks, especially on concrete surfaces. The dew claw attaches to the paw by a loose flap of skin. The person who is cutting the dog's claws should pull the dew claw away from the leg and cut the claw without cutting into the blood vessels found in the quick. If the quick is cut, the dog may suffer pain and bleeding.
Some breed standards, such as the Beauceron and Great Pyrenees, indicate the dew claws must stay in place if the dog is going to be entered in dog shows. Otherwise, a veterinarian will often remove the dew claws when the puppy is between two and five days old, when the bones are soft enough to clip without discomfort for the puppy. If removal is delayed beyond five days, the veterinarian will most likely wait until the puppy is old enough to be anesthetized for the procedure. The decision to remove the dew claws is an individual one that is decided by the owner based on the breed of dog, and their individual preferences.
According to a study performed by Clyde E. Keeler and Harry C Trimble published in the "Oxford Journal of Heredity", the dew claw was more prominent in earlier generations of dogs. It has changed during evolution because it is not a vital function to the dog. The authors theorize that earlier dogs that had to hunt for prey had more use for the dew claws. Through domestication, dogs found less use for the dew claw, and it became less prominent on their paws.