The Collaborative International Dictionary of English v.0.48:

Inchworm \Inch"worm`\, n. (Zool.)
   The larva of any geometrid moth. It progresses forward by
   first bringing the rear end of the body forward, forming a
   loop, then moving the front part of the body; called also
   measuring worm, measuringworm, spanner, and looper.
   See Geometrid.
   [1913 Webster]