tick, mite
螕 centers on small parasitic arachnids: ticks and mites. The meanings are closely related, both referring to tiny blood-sucking or skin-infesting creatures.
螕 combines 虫 (insect/creature) with a phonetic component that likely contributed the sound. The exact historical development of the right side is uncertain.
The insect radical 虫 on the left suggests a small creature. Picture a tick or mite, a tiny bug that clings to skin.
For ヘイ, imagine a tick crawling toward a hay bale: hay -> ヘイ, and the tick hides in the hay.