The Collaborative International Dictionary of English v.0.48:

Wriggle \Wrig"gle\, v. i. [imp. & p. p. Wriggled; p. pr. & vb.
   n. Wriggling.] [Freq. of wrig, probably from OE. wrikken to
   move to and fro; cf. LG. wriggeln, D. wrikken, Sw. vricka,
   Dan. vrikke.]
   To move the body to and fro with short, writhing motions,
   like a worm; to squirm; to twist uneasily or quickly about.
   [1913 Webster]

         Both he and successors would often wriggle in their
         seats,
         as long as the cushion lasted.           --Swift.
   [1913 Webster]

WordNet (r) 3.0 (2006):

wriggling
    adj 1: moving in a twisting or snake-like or wormlike fashion;
           "wiggly worms" [syn: wiggly, wriggling, wriggly,
           writhing]