Army worm was the term applied to extortionists who followed the invading Federal army in the South during the Civil War.

Additional Resources:

"The 'Army Worms'--their Unholy Crusade, &c." The Daily Dispatch [Richmond, Va.]. November 25, 1861. http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A2006.05.0331%3Aarticle%3Dpos%3D46 (accessed October 15, 2012).