This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Jorogumo (Japanese)
Jorogumo is a type of creature of Japanese folklore. It can shapeshift into a beautiful woman, so the kanji that represent its actual meaning are 'woman-spider'; the kanji which are used to write it instead, 'entangling newlywed woman' have a jukujikun pronunciation that is related to the meaning, but not the sound of the word. In Toriyama Sekien's Gazu Hyakki Yagyo, it is depicted as a spider woman manipulating small fire-breathing spiders.
It can shapeshift between a three forms: a giant spider, a human woman, half woman/half spider. It transforms into a human woman to seduce and entrap humans to eat, however its reflection will show its true spider form. It can not be killed by any kind of poison. Described as a half-woman/half-spider surrounded by her spider children. Their body size averages between two to three centimeters long, but they can grow much larger as they age; some are large enough to catch and eat small birds.