I'm not entirely sure about this myself as my japanese is not very good. But for the usage of 'squirm' vs 'wriggle', they both describe a similar thing but wriggle refers more to the twisty motion as you described. もじもじする sounds closer but i will let somebody else be the judge of that :) Example 1: The worm wriggled across the soil. Example 2: The restrained girl, struggled and squirmed to try to break free. Example 3: At the party, i danced and wiggled my bum Example 4: As my friend held the spider close to me, i squirmed as i hate spiders!