Dewclaw

July 09, 2022

When I played with our previous dog Bella, I was often scratched by the small claw spaced about three inches above both of her front paws.  I wondered why this claw was there as it did not seem to serve any purpose.  When I asked Melissa about the claw, she said it was often vestigial in small breed dogs, and some owners have them surgically removed.  Melissa had not and said others warn against removal as this can be painful.  Now that we have Zena, I found she not only has the claw above her front paws, but also on both rear paws as well.  Again, the only purpose I have seen for this claw is to scratch us when Zena jumps into your lap (yes, she is a 50 pound lap puppy).  Melissa said this was called a dewclaw.

When I looked online, I found a dewclaw is a digit on the foot of many mammals, birds, and reptiles.  This claw commonly grows higher on the leg than the rest of the foot and does not contact the ground when the animal is standing.  The name refers to the dewclaw’s alleged tendency to brush dew away from the grass.  Dogs almost always have dewclaws on the inside of the front legs and occasionally also on the hind legs.  Unlike front dewclaws, rear dewclaws tend to have little bone or muscle structure in most breeds.  It is normal for certain breeds to have more than one dewclaw on the same paw.  At least one of these dewclaws will be poorly connected to the leg and is often surgically removed.  For certain dog breeds like the Beauceron used for herding sheep in France, a dewclaw is considered a necessity as it helps the dog navigate snowy terrain.  There is some debate about whether a dewclaw may help dogs gain traction when they run.  In some dogs, the dewclaw contacts the ground when they are running and the nail on the dewclaw often wears down the same way the nails on their other toes do.  In other dogs the dewclaw never contacts the ground, and the nail never wears away, and it is often trimmed to maintain the claw at a safe length.

The dewclaw is not a dead appendage.  They can be used to lightly grip bones and other items the dog holds with its paws.  In some dogs, these claws may not appear to be connected to the leg except by a flap of skin, and the claw does not have a use for gripping, as the claw can easily fold or turn.  Others suggest dogs like the Great Pyrenees (Zena) use the dew claw to aid climbing on rocky mountain slopes.  The dewclaw is also used by the dog to scratch itself to remove irritants from around eyes, ears, and fur. The technical term for these additional digits on the rear legs is hind-limb-specific preaxial polydactyly (now you know).  Several genetic mechanisms can cause rear dewclaws; they involve the LMBR1 gene and related parts of the genome.  Rear dewclaws of the mountain dogs do have phalanx bones and can be used for a variety of purposes.  Dewclaws are also recognized as the breed standard for the large shepherd dogs by the American Kennel Club as well as Britain’s Kennel Club.

THOUGHTS:  While a dewclaw may seem superfluous for smaller breeds of dogs, they appear to provide an advantage for large breeds that typically navigate rough or snowy terrain.  A similar vestige is evident with some larger snakes who have stunted legs beneath their skin and tiny, claw-like spurs on each side of the single opening where waste and reproductive fluids exit the body (the cloaca), which include remnants of what used to be leg bones.  Male snakes use these spurs during courtship and for fighting, but not for locomotion.  There is a common belief that the human appendix is a vestigial organ, but recent research has shown the appendix has several important immune effects in the womb and as an adult.  Whether a dewclaw, the spur on a vestigial leg, or an appendix, what we keep finding is that the answer is, “I do not know.”  The ability to admit what is not known and question what is known is the essence of the human quest for understanding.  That also works for understanding other people.  Act for all.  Change is coming and it starts with you.