'armyworm' originates from English, specifically the compound of 'army' and 'worm', where 'army' ultimately came via Old French 'armée' (from Latin 'armāta') meaning 'armed force' and 'worm' comes from Old English 'wyrm' meaning 'serpent' or 'worm'.

'armyworm' changed from the older hyphenated form 'army-worm' used in earlier English descriptions of pest outbreaks and eventually became the modern English word 'armyworm'.

Initially, it referred generally to any 'worm' or caterpillar that moved in masses like an army; over time it evolved into its current, more specific meaning of certain pest caterpillars (larvae of particular moth species) that travel and feed in large groups.