Never thought of caterpillars as contorted, but I like the simile.  Hope you do too, and the image I used. As contorted a caterpillar as I could find and what a lurid green!

‘… contorted like caterpillars.’  22 April 1855

For another caterpillar wriggling metaphor, see George Eliot’s.

Source: Henry David Thoreau, The Journal 1837-1861, Damion Searls (ed.), preface by John R. Stilgoe (New York: New York Review Books, 2009), p. 321

Photo credit: Josch13