The word "蚕蛹" is formed by combining the character "蚕", meaning silkworm, which is a pictograph derived from the shape of the insect, with the character "蛹", meaning pupa, which uses the insect radical "虫" to denote its category and the component "甬" primarily to suggest pronunciation. Together, these characters create a compound term that directly specifies the silkworm pupa.