This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
蚖 combines 虫 (insect/reptile) with 元, which likely contributes the sound. The exact historical development is uncertain.
The insect radical 虫 suggests a small creature, but without a clear meaning, picture a mysterious bug with the sound 元 (origin) as its name.
For ゲン, imagine a genie emerging from a bug-shaped lamp: genie -> ゲン, and the insect radical 虫 hints at the creature's form.