Werewolves are an extinct species since the 19th century. Members of the species were essentially human for the most part, but once a month, on full moon, they would transform into a large, bloodthirsty wolf. Once the full moon went down, they would morph back into a human. Unlike vampires, werewolves saw their primal nature as a curse rather than a gift and sought to not reproduce, to avoid passing on the condition.
Since their transformation only occurs once a month, werewolves had an easier time controlling their condition than vampires. However, there is no serum to prevent the transformation like there is for vampires.
Typically, they would experience headaches on the evening of the full moon. By nightfall, they would start getting cramps. Then, at the rise of full moon, they would have to experience the agony of growing limbs, and teeth. Their fingernails would fall out, to be replaced by long, sharp claws. Thick hair would sprout from their skin. The jaw dislocates, fangs splitting the gums, skin stretching over a newly formed muzzle. Their entire body structure is reformatted to that of a wolf. The transformation is characterised by a lot of screaming. They would remain as a wolf for three hours until they turned back into a human.
Behaviour and Abilities
In their human form, werewolves were generally good people. They despised themselves for their wolfish side and tried to fit in as best they could. They did not possess any superhuman strength like untransformed vampires do.
Once transformed, the wolf would not retain any of its human nature. Even more savage than a normal wolf, the werewolf would actively hunt and attack humans to satisfy its bloodlust. Werewolves did not appear to be stronger than a normal wolf but their sheer savagery made them threatening opponents nonetheless. If not wanting to kill the werewolf, the best way to apprehend them is with a tranquilliser. However, the tranquilliser will not work if introduced before or during the transformation, as the adrenaline will flush out any toxins in the body. The only things guaranteed to kill a werewolf are silver bullets or decapitation (which kills most things (apart from zombies)).
Even though werewolves tried not to pass on their condition, a very small population today still have werewolf genes. However, the infection has been diluted down through the generations and is too weak to manifest in an actual transformation.
The exception was Ed Stynes, a mortal whose diluted werewolf genes had never caused a problem, but after being given magic by Argeddion, Ed's transformation was triggered. Skulduggery Pleasant and Valkyrie Cain apprehended him and managed to take him down. Ed woke up in the Medical Wing of the Sanctuary, back in his human form. After The Summer of Light, it is assumed that the magic within him returned to Argeddion, thus freeing him from being a werewolf.