The Collaborative International Dictionary of English v.0.48:

Squirm \Squirm\ (skw[~e]rm), v. i. [imp. & p. p. Squirmed
   (skw[~e]rmd); p. pr. & vb. n. Squirming.] [Cf. Swarm to
   climb a tree.]
   To twist about briskly with contortions like an eel or a
   worm; to wriggle; to writhe.
   [1913 Webster]