The insect/creature radical, placed left. It signals the character names a small animal - here a toad. The same radical groups 蛙, 蛇, and 蟆 into one semantic family of crawling and creeping creatures.
Carries the sound. The reading has drifted from mò to má, so today it is only a loose phonetic anchor, but it still links 蟆 to other characters built on this same right-side element.
