This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
蟎 is a rare character combining 虫 (insect) with 㒼, which likely contributes a phonetic element. The exact historical development is uncertain.
The insect radical 虫 suggests a bug or small creature, but without a clear meaning, picture a mysterious bug hiding under the complex right side.
For だに, imagine a tick (ダニ) crawling on the insect radical 虫: ダニ -> だに, and the bug is a tick.
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