Shape-shifter

Appearance
The wolves themselves vary in physical appearance, just like their human counterparts. For example, the wolf that scares Laurent away from Bella Swan is described as: “enormous—as tall as a horse, but thicker, much more muscular. The long muzzle grimaced, revealing a line of dagger-like incisors. A grisly snarl rolled out from between the teeth, rumbling across the clearing like a prolonged crack of thunder.” So huge that Bella, along with other residents of Forks, even mistakes it for a "bear" at first.

The other wolves are described: "One was a deep gray, the other brown, neither one quite as tall as the first." And finally a "rusty brown monster".

It is this "reddish brown" wolf that Bella focuses on, explaining "The wolf's eyes were dark, nearly black. It gazed at me for a fraction of a second, the deep eyes seeming too intelligent for a wild animal. As it stared at me, I suddenly thought of Jacob," but it is not until her later dream that Bella realizes that these eyes are actually "the black-brown, familiar eyes of Jacob Black."

Each wolf is a different color, which the stories say correlates with each wolf's true self. Quil Ateara and Sam Uley joke with one another that Sam's black fur is connected to his "black heart" while Quil's chocolate-brown fur reflects how "sweet" he is. This is more or less the only explanation offered for why each of the wolves are so radically different in coloration.

In Eclipse, we discover that there are some correlations between human and werewolf form. Bella asks why Jacob is furrier than the others: "Because my hair is longer."

The "monstrous size" of these creatures is emphasized again and again. This links clearly with the actual changes in the boys as well, which Bella notes, although she doesn’t connect the two together until later. "These were just four really big half-naked boys." As a human Jacob is at least 6' 7", and she also remarks of the changes in Quil: "He looked bigger than the last time I’d seen him. What was with these Quileute boys? Were they feeding them experimental growth hormones?" It seems that a period of rapid growth happens in the human boy before he becomes a wolf.

It is also noticeable that the human form changes when the werewolf mutation begins to occur. The mutation makes the boys' bodies accelerate to that of a full grown man, with the aging stopping at around the physical age of 25. This aging will pause at this point until the man stops taking on the spirit wolf form. Jacob crops his hair short, just like Sam and the others, but, "The planes of his face seemed to have hardened subtly, tightened...aged. His neck and his shoulders were different, too, thicker somehow. His hands, where they gripped the window frame, looked enormous, with the tendons and veins more prominent under the russet skin." Becoming a wolf is a sign of maturity, and he visibly ages as a human as well. This also seems to be true of Sam Uley, as his first description is: “closer to a man than a boy, and his voice was very deep."

The boys become very similar in their physical human appearance until they could be mistaken for "quadruplets" as there was "something about the way they moved almost in synchronization to stand across the road from us, the way they all had the same long, round muscles under the same red-brown skin, the same cropped black hair, and the way their expressions altered at exactly the same moment."

Speed
Like the vampires, werewolves are also superhuman in their ability to run. Jacob even compares it to being better and faster than a motorcycle, and thinks that the ability to run so fast is "the best part" of being a werewolf.

Even in his human form, Jake seems to have developed more speed: "Then he turned and sprinted through the parking lot, across the road, and into the bordering forest. He flitted into the trees, swift and sleek as a deer."Jake noted in Breaking Dawn that running would be faster than riding a motorcycle. The comparison to the vampires here is quite clear and Bella herself notes that being on Edward's back as he runs is "a hundred times better than the motorcycle."

As the wolves could catch Laurent it appears that they are even faster on their feet than the vampires are. Bella says: "I couldn't imagine that—the wolves running faster than a vampire. When the Cullens ran, they all but turned invisible with speed." This may have to do with the werewolves being quadrupeds (using four feet to run) as opposed to vampires who are bipeds. It seems that speed is their real weapon, along with the exchange of thoughts within the pack.

Their reflexes are also immensely fast: "With stunning speed, Jacob yanked a can opener from the counter and launched it at Jared's head. Jared's hand flicked up faster than I would have thought possible, and he snagged the tool just before it hit his face." Also in Eclipse, at the Quileute bonfire, Paul harassed Jacob to give him his hot dog. When Jacob flung it across the circle, Paul caught it before it land hot-dog-first in the sand. They are certainly quick enough to tear apart one vampire as a pack, regardless of how strong that vampire is.

Strength
Their movement is in "powerful bounds" as a wolf, but also as a human there seems to be a difference in strength. Bella notes that Jake handles her "too roughly" and when he hugs her it's with a "crushing" movement so that Bella "can't – breathe." He doesn't seem aware of his additional strength like the vampires are, but this could well be due to the newness of the changes he has experienced.

Like the Cullens, once Jacob is a wolf, he exhibits similar displays of strength: "He slid his arms under me and lifted me without effort—like picking up an empty box." However, before the transformation has happened he is restricted to putting his arm around Bella and helping her back along the trail after her motorcycle accident.

When Jacob discusses being a wolf with Bella later in the novel, he explains: "It's what we're made for, Bells. We're strong, too."

The sounds that the wolves make are also linked with both strength and ferocity, for example, their growls are described repeatedly as "like thunder".

Part of the strength of a werewolf is that he (or she) is not a single entity, but part of a pack. They are stronger as a group than they would be alone. They communicate through the fact that they "hear each other's thoughts, but only when you're wolves", and during fights, like those we see at the end of Eclipse they can alert each other of danger.

They are more than a team. There is "no privacy, no secrets" between them and this makes them stronger. As Edward puts it, "The pack mind is mesmerizing. All thinking together and then separately at the same time. There's so much to read."

Physiology
The skin when they are in human form is "burning hot". Bella feels this first when she believes Jake has a fever on the way home from the trip to see the movie. "Whoa, Jake—you're burning up!" but it is common enough for his body to be consistently at this temperature. Werewolves are clearly the polar opposites of the vampires, with their icy-cold touch and marble-like skin. Perhaps their physiological make up reflects the tension between them.

"We run a little warmer than the normal people. About one-oh-eight, one-oh-nine. I never get cold anymore. I could stand like this" —he gestured to his bare torso— "in a snowstorm and it wouldn't bother me. The flakes would turn to rain where I stood." Stephenie Meyer says this is one of the unique features of her werewolves.

They are also able to heal very quickly physically. Injuries don't last very long at all.

The actual transformation between human and werewolf is described in most detail in New Moon. Certainly the initial transformation is not an easy one, as Jake explains his symptoms to Bella: "Everything," he whispered. "Every part of me hurts." Initially, I thought that this must be physical pain that Jake was experiencing, but Stephenie explained that this wasn’t actually the case. "The transformation into the wolf form is not a painful process, only disorienting and mentally uncomfortable." It is mental pain that Jake is referring to, from the fact he has realized that he is both a monster and the implications this has in his relationship with Bella.

Their skin is very strong though not granite hard like a vampire's, the durability and heal factor makes it easier in a fight with the enemy.

Tattoo
In the movie New Moon, the members of the pack all wear this tattoo:

http://i199.photobucket.com/albums/aa11/cammochick00/twilight/quiluetetatoo.jpg

Phasing
The transformation itself can happen at any time, and isn't dependent upon a full moon. In young werewolves cases, they can change involuntarily because of lack of self-control: "'What would happen...if you got too mad?' I whispered. 'I'd turn into a wolf,' he whispered." The effects of this sort of transformation is shown in the relationship between Sam and Emily and the disfiguring injuries she has suffered.

Transformation or "Phasing" is a sudden process and is described through a series of violent words: "burst", "exploded", "vibrating violently", "ripping", "blasted". It is so sudden "that if I'd blinked, I'd have missed the entire transformation" Initial transformations seem to be triggered by anger, and Jake explains that his own conversion to becoming a werewolf was staved off by his happiness with Bella: "I was like a time bomb. You know what set me off? I got back from that movie and Billy said I looked weird. That was all, but I just snapped. And then I—I exploded. I almost ripped his face off—my own father!". Sam Uley's transformation also supports this, as it "took him two weeks to calm down enough to change back."

Jacob's point of view explains the transformation back into human form: "I ignored him [Jared], closing my eyes and pulling myself together again. It felt like the air was trembling around me, shaking out from me in small waves. I lifted myself up on my hind legs, catching the moment just right so that I was fully upright as I shimmered down into my human self."

Jacob seems to find phasing between wolf and human form easier than most. "Even Sam couldn't have phased on the fly like that. He saw Paul losing it, and it took him, what, half a second to attack? The boy's got a gift." He explains later to Bella that this may be due to his ancestry: "It takes some practice to phase back and forth but it's easier for me… because Ephraim Black was my father's grandfather, and Quil Ateara was my mother's grandfather." Because his lineage is so very strongly linked with the last pack, it seems to be easier for him than most.

Jacob can also seem to phase when he isn't angry, as seen in Breaking dawn when he was racing Renesmee to see who could get the biggest catch. Whether this is because vampire Bella was with them, or because Renesmee's a vampire hybrid is unknown. It's probably just his lineage that allows him.

Creation
Werewolves are only created when there are neighboring vampires, so that the Quileute land is always protected. Jacob explains, "There's no exact age...it just builds and builds and then suddenly—" It seems to occur around the point where the boy becomes a mature man, and is certainly accompanied by a sudden growth spurt that lasts for two months.

Their sense of pack-identity is strong. So much so that they are capable of hearing "thoughts—each other's anyway—no matter how far away from each other we are. It really helps when we hunt, but it's a big pain otherwise. It's embarrassing—having no secrets like that." Even in wolf form, they retain full control of their human minds. "They are still themselves–not at all the feral, mindless werewolves of other mythologies." This means that all actions are knowing actions, although it is entirely possible for a werewolf to lose his temper and for him to be out of control as both a human and a wolf. Jacob shows his human side in wolf form on the run up to the fight with Victoria, when he pulls a face with "his tongue lolled out the side in a wolfy grin" to make Bella giggle. "Jacob's grin widened over his sharp teeth."

Werewolves were believed to be only male until the transformation of Leah Clearwater, which surprised everyone, even though "she's a direct descendant, all right."

Imprinting
The issue of imprinting is also critical as this is how the shapeshifter finds a soulmate: "It's not like love at first sight, really. It's more like... gravity moves. When you see her, suddenly it's not the earth holding you here anymore. She does. And nothing matters more than her."

Once two people are imprinted, the shapeshifter will feel the need of constant being in his soulmate's presence and to unconditionally give her whatever she wants, and vice versa. Should the imprinted one be an infant, the shapeshifter will act as a big brother figure; romantic feelings will not grow until the imprinted one comes to age.

Imprinting doesn't only work on humans but on hybrids as well. Half human/vampire hybrids. Like Jacob, it's certain that if a shapeshifter imprints on a hybrid, their hatred for their enemies (vampires) will be gone.

In addition, there is a law in the Quilete tribe that whoever becomes imprinted by a member of the pack, the rest of the wolves will not be allowed to harm her. This law is to prevent unnecessary battle as the shapeshifter will not forgive whoever harmed his soulmate.

Senses
Their sense of smell has adjusted to help them identify their one enemy. "Vampire," he spit out. ..."I can smell it! Dammit!" It is not clear whether it is heightened in other circumstances, but they certainly know vampires from a distance and find the smell sickly sweet and repellent.

They have sharp eyes that can see for great distances.

Like vampires, they are also very strong; Bella breaks her hand punching Jake: "It was broken, I could feel it."

They all have excellent hearing even when in their human form. In Breaking Dawn, Jacob was able to hear Quil playing with Claire at First Beach from his bedroom.

Genetics
Finally, someone has the wolf inside them for life: "What I am was born into me" (EC4), and while they are still mostly wolfish, they "can't... grow up," and stop aging. Jacob explains that this is only until they “stop phasing for a solid length of time [then] we age again." It is unknown how long that period of time is before they can start ageing again is.

It is while Carlisle is treating Jacob that he takes a blood sample and does tests with it, on the claim that he is fascinated by "werewolves". It is then that he finds out that shape-shifters have 24 pairs of chromosomes, 1 more pair than a human and 1 less than a vampire.

Werewolves vs. shape-shifters
While talking to the Volturi in Breaking Dawn, Edward reveals that the wolves of La Push are actually "shape-shifters" and not true werewolves. The original Quileute shape-shifters apparently could have taken the form of any animal, but chose wolves. It is unknown if the Children of the Moon share the same attributes as the wolf shape-shifters. At the bonfire in Eclipse, the Quileutes say that shape-shifters are a natural enemy of vampires when telling their legend of the original tribe of shape-shifters who suddenly felt antagonism when they smelled a vampire's scent.

It is unknown whether there are other kinds of shape-shifters besides wolves.

The Quileute packs
In Breaking Dawn, Seth is informed that Bella and Edward have returned home and Bella has a rare disease. Jacob soon finds out that, instead, Bella is pregnant with Edward's half human-half vampire child. Sam and the others fear the harm the child brings and plan to kill all the Cullens including Bella and her mutant spawn. Jacob and Seth disband from the pack and form their own in order to protect the Cullens. They are soon joined by Seth's sister, Leah, in attempt to get away from Sam and protect her brother. After the birth of Renesmee, Jacob imprints on Renesmee and the shape-shifters' feud with the Cullens is put to bed and both packs work together in helping the Cullens and protecting La Push and Forks.

Sam Uley's pack

 * Sam Uley - Alpha
 * Paul
 * Jared
 * Collin
 * Brady

Jacob Black's pack

 * Jacob Black - Alpha
 * Leah Clearwater - Beta
 * Seth Clearwater
 * Embry Call
 * Quil Ateara