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