the earthworm
螾 centers on the earthworm as a specific creature. The meaning is narrow and concrete, referring to this particular animal.
螾 combines 虫 (insect/creature) with 寅, which likely contributes the sound イン. The character was used specifically for the earthworm.
The left side 虫 indicates a small creature, and the right side 寅 looks like a worm burrowing through soil. Together they form the earthworm.
For イン, imagine an earthworm wriggling into an inn: inn -> イン, and the worm finds a cozy place in the soil.