This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
蚈 combines 虫 (insect) with 开, but the exact historical development is uncertain. It may have originally referred to a type of insect, but no clear meaning survives in modern usage.
The insect radical 虫 beside 开 suggests a bug, but without a clear meaning, picture a mysterious insect that has yet to be identified.
For ケン, imagine a scientist named Ken discovering this unknown insect: Ken -> ケン, and he carefully studies the bug.