Spanworm is a term used to refer to the larva of certain species of moth that are known for their looping crawling behavior. If you are looking for synonyms for the word spanworm, you can consider using "inchworm," "looper," or "measuring worm." The term inchworm is quite popular as it describes the movement of the larva; they move in a way that looks like they are measuring the ground with their bodies. The term looper refers to their looping behavior, while the term measuring worm is used to describe their methodical crawling approach. These synonyms can be used interchangeably depending on the context of the discussion.