This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
蟙 combines 虫 (insect) with 戠, which likely contributes the sound. The exact historical development is uncertain.
The insect radical 虫 suggests a bug-related meaning, but the kanji is too rare for a reliable mnemonic. Its meaning is unclear.
For ショク, imagine a rare insect that makes a 'shock' sound when it moves: shock -> ショク, and the insect radical 虫 hints at the bug.