Insect radical on the left — also
蛇's indexing radical (Kangxi #142). In classical use
虫 covered any small creeping creature (insect, reptile, worm), so it sits naturally with snakes. Same radical in
蚊 (mosquito),
蜘 (spider),
蜂 (bee),
蝶 (butterfly),
蜥 (lizard) — the entire creepy-crawly family.