Bottom insect radical - originally a coiled snake, generalized to small creatures including crustaceans. Carries the meaning: 螯 names the large grasping pincer of crabs, lobsters, and scorpions. Same indexing radical as 蟹 crab, 虾 shrimp, 蛇 snake.
Top 敖 supplies the sound - áo stays áo with no shift. Originally a person striding with a raised hand (carefree wandering), but in 螯 that meaning is silent and 敖 acts as a pure phonetic tag. Same family: 熬 to simmer, 翱 to soar, 嗷 to wail, 鳌 sea-turtle.
