This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
蜞 combines 虫 (insect) with 其, which likely contributes the sound. The exact historical development is uncertain.
The insect radical 虫 suggests a creature, but the overall meaning is unclear. Picture a rare, unidentified bug with the shape of 其 on its back.
For キ, imagine a key-shaped insect: key -> キ, and the bug 蜞 is the key to an ancient mystery.