Purpose of Dew claws?

Something I have often wondered about - what do cats use their dew claws for? I have never seen a cat using them. And if they don't use them, then why did they evolve? They must have had a purpose once. The only thing I can think of is keeping prey still with claws facing in opposite directions. Does anyone have any biological knowledge to share?

Thank you for asking the question, Jenny. I've often wondered the same thing.

I've seen cats hold down prey using their dew claws, and had my fingers held on to with them, so I assume that's the purpose. I've always thought of them as cats' thumbs.

lol i was wondering what a dew claw even was! but if youre talking about their little thumb claw i would just assume they use it like we do, to hold stuff. jericho uses his to clamp onto me if i start to get my hand free of his other nails

The most plausible reason IMO is merely because cats are part of the mammalian tetrapod genus evolved from lobe finned fish, and nearly all still retain five digits through shared ancestry (lizards, frogs, whales, bats, dogs, etc all have a humerus, ulna/radius, carpals, with five toes/fingers). To an alien species, we all probably just look like different versions of a shared theme since we're very similar configurations from blood, to heart design, spine, ribs, teeth, two eyes and ears, nose, tongue, nails, etc when you get down to it. Heck, med students often work on pigs for training since inside they are so similar to us.



So the question is not so much why they have a fifth claw, but why it isn't extended up front with the other four, and I would wager simply because there isn't enough room, just like with the bat wing:


Recall that in evolution, if a particular trait is not a significant benefit or hindrance, the trait can continue to be passed generation to generation as there is no strong force for change. It is a small genetic change for a limb to get thicker/slimmer or longer/shorter, but to completely disappear is major. Whale skeletons still retain a useless small hip bone for example, so some adaptations are clearly very slow to change.

My cats wrap their front paws around toys, and the dew claw provides much better grip and traction as it is further back on the arm. It acts basically as a pincer to keep the toy immobilized long enough for one of my cats to bite it's "neck" or bunny kick it. I've had a hard time wrestling toys free from my cats when they have their dew claws ni them.

Having been grabbed and pulled in for the bite, I think they are used to have a better grip on prey, a circle of claws that make escape harder.

There's a tad bit of dexterity in a cat's dew claws, some cats have more than others. They use them like thumbs to a small degree to help hold things.

I wish I had a video camera as my Tanna is a great example of this. She's quite "handy" with her front paws and regularly uses them to pick things up- often one pawed. When she does this she uses the dew claw to help "cup" whatever she is grabbing.

I imagine, though, that the miacids used the dew claw more so thats why the species evolved out of it have it and depending on the species, use it very much (such as raccoons).

In cats, the "thumbs" (I have never thought of them as dew claws in cats, LOL) are used for holding prey and to aid in climbing (I'm pretty sure a cat without "thumbs" couldn't climb very quickly). Also, as mention already, to "scoop" things up. In dogs, dew claws are used to stabilize the leg when the dog is running/turning quickly (this is why you'll never see anyone remove the dew claws from a working sheepdog). Some studies show that Agility dogs who have had their dew claws removed have a much higher incidence of arthritis and injury in their front legs.

Of course, both cats and dogs can manage without their "thumbs", but they aren't useless by any means.

Originally Posted by Willowy

In dogs, dew claws are used to stabilize the leg when the dog is running/turning quickly (this is why you'll never see anyone remove the dew claws from a working sheepdog). Some studies show that Agility dogs who have had their dew claws removed have a much higher incidence of arthritis and injury in their front legs.

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Ehhhh... I find that unlikely, and haven't ever seen a source that supports that. I'd wager thats one of the myths perpetuated by groups that are opposed to unnecessary surgery on animals as a form of cruelty (since dewclaw removal is somewhat common-place due to concerns of scratching people or getting caught on things like chain fences and the like), rather than there really being any true science behind it.

Originally Posted by Ducman69

The most plausible reason IMO is merely because cats are part of the mammalian tetrapod genus evolved from lobe finned fish, and nearly all still retain five digits through shared ancestry (lizards, frogs, whales, bats, dogs, etc all have a humerus, ulna/radius, carpals, with five toes/fingers).

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Well, that makes sense, but where is the 5th claw on the rear paws? Do cats have some type of tiny, vestigial 5th claw on their rear paws or has it vanished completely?

Actually the dew claws in dogs are vestigial.
They used to have the same purpose as a cat's dew claws, but dogs evolved to run rather than climb trees, rendering their dew claws useless.

Originally Posted by Grogs

Well, that makes sense, but where is the 5th claw on the rear paws? Do cats have some type of tiny, vestigial 5th claw on their rear paws or has it vanished completely?

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No fifth toe on the rear legs of canids (except as a defect), I worded that poorly.

I'd wager that a rear dewclaw is perhaps more apt to get caught up on something and tear when running through brush since they push off hardest from their rear legs, and so perhaps that is why it disappeared more quickly than the fronts. Or as was mentioned perhaps there is limited functionality left in the front dewclaws for manipulating objects.

Originally Posted by Ducman69

Ehhhh... I find that unlikely, and haven't ever seen a source that supports that. I'd wager thats one of the myths perpetuated by groups that are opposed to unnecessary surgery on animals as a form of cruelty (since dewclaw removal is somewhat common-place due to concerns of scratching people or getting caught on things like chain fences and the like), rather than there really being any true science behind it.

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The vast majority (I would say all. . .but there's bound to be a rebel somewhere, right?) of working Border Collie breeders will NOT remove front dewclaws (rear dews are rarely well-attached and so are removed to prevent injuries). Front dews are consider quite beneficial to the BC's job. I doubt they're a bunch of AR fanatics, if that's what you're getting at. Removal might be fine for housepets and hunting dogs who run through the underbrush, but for dogs whose jobs require sharp turns, it's just not done. (Also another reason for the working BC people to hate on the AKC. . .since AKC standards require dewclaw removal for BCs. Thus strengthening the "Barbie Collie" accusations)

Here's a thing from a vet who did x-rays on performance dogs with dewclaws removed. I don't think there have been any actual studies done, though. Ignore the blog; I couldn't figure out how to link directly to the pdf from my phone, and this blog is the only one thing I could find that had it printed out. There is a link to the pdf on the blog: http://blog.tiganagoldens.com/?p=54

Cats have always had dew claws, the equivalent of our thumbs.  Our ancient ancestors the earliest reptiles had five digits and all four-legged mammals have the equivalent of the same.  Some have evolved into hooves, trotters and even three-toed "hands" but the vestiges of these earlier digits can still be found in all those animals.

Even we have the vestiges of tails and appendixes amongst other remnants.

I think that the dew claw on a cat is usually a totally useless bit of kit even if some do seem to find them useful.

A bit of history:  cats and dogs both evolved from a common ancestor tens of millions of years ago.  That ancestor probably didn't look much like either a cat or a dog but it certainly had all the main features of all modern mammals.  There really isn't much difference between any of us  -  only in the way we look and behave.

My dog may as well have her dew claws removed... she's chewed them off before and is beginning to again now that they've grown back.

My cats have used their dew claws to grab my fingers before and pull me to them, as well as scoop up toys when playing. I enjoyed reading the histories and knowledge of them though because I really never thought of what they were really meant for

I have yet to see any of my cats (we have 6 at the moment) actually try to "use" their dew claws.  They seem to have no control whatsoever over them and all they seem to do with them is to get caught up in clothing etc and then try to shake themselves loose from it. 

They no longer have effective muscles to move the claws as far as I can tell, though I have seen reference to ligaments in dogs' dew-claws. They are certainly not firmly attached to the main bone in the paw.  In addition to which, why should an animal prefer to *use* a pretty useless item when it has four other very effective ones?

Perhaps Googling *cat biology* might mention it.

I just did and found this:

A dew claw on a cat is an example of a vestigial structure because over time, they have lost their purpose and are not necessary to the cat’s survival. At one point in time it may have been located lower on the foot and used for balance, or as an extra claw for hunting and killing pray. However, as cats evolved, the dew claw moved farther up the leg and no longer has any purpose.

It's a school website and I imagine they found the information from a bona fide expert source.  I've run out of time :-)

http://saintsapbiology.wordpress.com/author/ochild14/