|Average height||Human-sized (usually)|
|Place of origin||Earth|
|Status||Depends on the type|
|Behind the Scenes|
|Created by||David Greenwalt and Jim Kouf|
Wesen are a large family of creature-types that live through the world, as a parallel society opposite humans. They have been historically hunted by Grimms.
Wesen are liminal beings, and have two distinct forms, as they alternate between a human form and a creature form. The process of shifting from one to the other is known as "woging". Although they can woge voluntarily, most Wesen also experience an involuntary woge triggered by emotional states such as stress or fear. This second type of woge is usually invisible to normal humans, who continue to perceive the Wesen in his or her human form; but it is visible to Grimms. All Wesen possess the ability to identify Grimms when in their woged state because when a Grimm looks at a woged Wesen, their eyes turn black with their pupils being an image of the Wesen. Woged Wesen always shift back to human form when they die.
Each Wesen, no matter the type, possesses two sets of DNA in each cell. Because of this, Wesen genetics are very complicated. If two Wesen have a child or a Wesen and a Kehrseite-Genträger have a child, there is a one hundred percent chance that child will be a Wesen. If a human and a Wesen have a child, there is a fifty percent chance that child will be a Wesen. Two humans or a human and a Kehrseite-Genträger cannot have a Wesen child. The chance of two Kehrseite-Genträgers having a Wesen child is unknown. When two different types of Wesen have a child, that child will be whichever type is dominant over the other.
In terms of basic biology, Hexenbiests seem to be the most atypical species, and there are indeed hints that they don't belong to the same category of beings as the others. The Force du Sang potion is explicitly stated to require the blood of "a Grimm, a Wesen, and a Hexenbiest"; suggesting that Hexenbiests might not have been considered a type of Wesen at the time the recipe was written. As stated above, unions between humans and Wesen don't typically spawn hybrids, but a union between a human and a Hexenbiest does, as demonstrated by Sean Renard.
Despite their variable natures, all Wesen are universally affected by certain drugs that have a different effect on them than they would on humans, and there are diseases that only affect Wesen. Some substances that are harmless to humans may have a poisonous, medicinal, or psychedelic effect on Wesen; or vice versa; and the effect often seems to be the same for all different kinds of Wesen. On the other hand, some physiological weaknesses may be specific to one kind only. A notable example is the Völlige Verzweiflung fungus, which only affects Blutbaden.
Behavior and Society
Every type of Wesen behaves differently and has a different societal structure. Most Wesen have a specific response to a encountering a Grimm, with most being afraid but some react with anger or even awe.
When Wesen grow old and are susceptible to suffering from dementia, they may start to woge in public, endangering humans directly and the entire Wesen community indirectly due to the risk of exposure. Because of the enormous risk that this represents, senile Wesen are traditionally euthanasiated by the Wesen community. This is typically done by family members or other Wesen contacting a Gevatter Tod, a.k.a. "Godfather of Death", a specialized insectoid Wesen which delivers a painless death.
Traditionalists among Wesen strongly oppose romantic relationships between different Wesen species; although some races, like Fuchsbau and Klaustreich, don't seem to have that much of a problem with it, as do at least some Seelenguter and Blutbaden. Some Wesen, such as Murciélagos and Siegbarste, have been shown to pursue relationships with humans. Species such as Ziegevolk, Spinnetod, Musai, and female Naiads, are specifically drawn to humans of the opposite sex for one reason or another (which usually doesn't end well for the human). The female Folterseele are similar, although with the difference that they don't go after humans, but tend to become victims of sexual assault due to the effect that they have on both humans and other Wesen, which tend to find them sexually attractive. Hexenbiests and Cupiditas are also infamous for their abilities to enchant others with love potions that make the victim completely obsessed with someone.
- While used by Monroe in the episode Stories We Tell Our Young, the exact meaning of the term Kehrseite-Genträger is unknown. Genträger is German for "gene carrier" resulting in many fans believing a Kehrseite-Genträger is a Human with recessive Wesen DNA